README
¶
Package ql is a pure Go embedded (S)QL database.
Installation
$ go get modernc.org/ql
Documentation: godoc.org/modernc.org/ql
Accompanying tool to play with a DB
Installation
$ go get modernc.org/ql/ql
Documentation: godoc.org/modernc.org/ql/ql
Documentation
¶
Overview ¶
Package ql implements a pure Go embedded SQL database engine.
Builders ¶
Builder results available at
https://modern-c.appspot.com/-/builder/?importpath=modernc.org%2fql
QL is a member of the SQL family of languages. It is less complex and less powerful than SQL (whichever specification SQL is considered to be).
Change list ¶
2020-12-10: sql/database driver now supports url parameter removeemptywal=N which has the same semantics as passing RemoveEmptyWAL = N != 0 to OpenFile options.
2020-11-09: Add IF NOT EXISTS support for the INSERT INTO statement. Add IsDuplicateUniqueIndexError function.
2018-11-04: Back end file format V2 is now released. To use the new format for newly created databases set the FileFormat field in *Options passed to OpenFile to value 2 or use the driver named "ql2" instead of "ql".
- Both the old and new driver will properly open and use, read and write the old (V1) or new file (V2) format of an existing database.
- V1 format has a record size limit of ~64 kB. V2 format record size limit is math.MaxInt32.
- V1 format uncommitted transaction size is limited by memory resources. V2 format uncommitted transaction is limited by free disk space.
- A direct consequence of the previous is that small transactions perform better using V1 format and big transactions perform better using V2 format.
- V2 format uses substantially less memory.
2018-08-02: Release v1.2.0 adds initial support for Go modules.
2017-01-10: Release v1.1.0 fixes some bugs and adds a configurable WAL headroom.
https://gitlab.com/cznic/ql/issues/140
2016-07-29: Release v1.0.6 enables alternatively using = instead of == for equality operation.
https://gitlab.com/cznic/ql/issues/131
2016-07-11: Release v1.0.5 undoes vendoring of lldb. QL now uses stable lldb (modernc.org/lldb).
https://gitlab.com/cznic/ql/issues/128
2016-07-06: Release v1.0.4 fixes a panic when closing the WAL file.
https://gitlab.com/cznic/ql/pull/127
2016-04-03: Release v1.0.3 fixes a data race.
https://gitlab.com/cznic/ql/issues/126
2016-03-23: Release v1.0.2 vendors gitlab.com/cznic/exp/lldb and github.com/camlistore/go4/lock.
2016-03-17: Release v1.0.1 adjusts for latest goyacc. Parser error messages are improved and changed, but their exact form is not considered a API change.
2016-03-05: The current version has been tagged v1.0.0.
2015-06-15: To improve compatibility with other SQL implementations, the count built-in aggregate function now accepts * as its argument.
2015-05-29: The execution planner was rewritten from scratch. It should use indices in all places where they were used before plus in some additional situations. It is possible to investigate the plan using the newly added EXPLAIN statement. The QL tool is handy for such analysis. If the planner would have used an index, but no such exists, the plan includes hints in form of copy/paste ready CREATE INDEX statements.
The planner is still quite simple and a lot of work on it is yet ahead. You can help this process by filling an issue with a schema and query which fails to use an index or indices when it should, in your opinion. Bonus points for including output of `ql 'explain <query>'`.
2015-05-09: The grammar of the CREATE INDEX statement now accepts an expression list instead of a single expression, which was further limited to just a column name or the built-in id(). As a side effect, composite indices are now functional. However, the values in the expression-list style index are not yet used by other statements or the statement/query planner. The composite index is useful while having UNIQUE clause to check for semantically duplicate rows before they get added to the table or when such a row is mutated using the UPDATE statement and the expression-list style index tuple of the row is thus recomputed.
2015-05-02: The Schema field of table __Table now correctly reflects any column constraints and/or defaults. Also, the (*DB).Info method now has that information provided in new ColumInfo fields NotNull, Constraint and Default.
2015-04-20: Added support for {LEFT,RIGHT,FULL} [OUTER] JOIN.
2015-04-18: Column definitions can now have constraints and defaults. Details are discussed in the "Constraints and defaults" chapter below the CREATE TABLE statement documentation.
2015-03-06: New built-in functions formatFloat and formatInt. Thanks urandom! (https://github.com/urandom)
2015-02-16: IN predicate now accepts a SELECT statement. See the updated "Predicates" section.
2015-01-17: Logical operators || and && have now alternative spellings: OR and AND (case insensitive). AND was a keyword before, but OR is a new one. This can possibly break existing queries. For the record, it's a good idea to not use any name appearing in, for example, [7] in your queries as the list of QL's keywords may expand for gaining better compatibility with existing SQL "standards".
2015-01-12: ACID guarantees were tightened at the cost of performance in some cases. The write collecting window mechanism, a formerly used implementation detail, was removed. Inserting rows one by one in a transaction is now slow. I mean very slow. Try to avoid inserting single rows in a transaction. Instead, whenever possible, perform batch updates of tens to, say thousands of rows in a single transaction. See also: http://www.sqlite.org/faq.html#q19, the discussed synchronization principles involved are the same as for QL, modulo minor details.
Note: A side effect is that closing a DB before exiting an application, both for the Go API and through database/sql driver, is no more required, strictly speaking. Beware that exiting an application while there is an open (uncommitted) transaction in progress means losing the transaction data. However, the DB will not become corrupted because of not closing it. Nor that was the case before, but formerly failing to close a DB could have resulted in losing the data of the last transaction.
2014-09-21: id() now optionally accepts a single argument - a table name.
2014-09-01: Added the DB.Flush() method and the LIKE pattern matching predicate.
2014-08-08: The built in functions max and min now accept also time values. Thanks opennota! (https://github.com/opennota)
2014-06-05: RecordSet interface extended by new methods FirstRow and Rows.
2014-06-02: Indices on id() are now used by SELECT statements.
2014-05-07: Introduction of Marshal, Schema, Unmarshal.
2014-04-15:
Added optional IF NOT EXISTS clause to CREATE INDEX and optional IF EXISTS clause to DROP INDEX.
2014-04-12:
The column Unique in the virtual table __Index was renamed to IsUnique because the old name is a keyword. Unfortunately, this is a breaking change, sorry.
2014-04-11: Introduction of LIMIT, OFFSET.
2014-04-10: Introduction of query rewriting.
2014-04-07: Introduction of indices.
Building non CGO QL ¶
QL imports zappy[8], a block-based compressor, which speeds up its performance by using a C version of the compression/decompression algorithms. If a CGO-free (pure Go) version of QL, or an app using QL, is required, please include 'purego' in the -tags option of go {build,get,install}. For example:
$ go get -tags purego modernc.org/ql
If zappy was installed before installing QL, it might be necessary to rebuild zappy first (or rebuild QL with all its dependencies using the -a option):
$ touch "$GOPATH"/src/modernc.org/zappy/*.go $ go install -tags purego modernc.org/zappy $ go install modernc.org/ql
Notation ¶
The syntax is specified using Extended Backus-Naur Form (EBNF)
Production = production_name "=" [ Expression ] "." .
Expression = Alternative { "|" Alternative } .
Alternative = Term { Term } .
Term = production_name | token [ "…" token ] | Group | Option | Repetition .
Group = "(" Expression ")" .
Option = "[" Expression "]" .
Repetition = "{" Expression "}" .
Productions are expressions constructed from terms and the following operators, in increasing precedence
| alternation
() grouping
[] option (0 or 1 times)
{} repetition (0 to n times)
Lower-case production names are used to identify lexical tokens. Non-terminals are in CamelCase. Lexical tokens are enclosed in double quotes "" or back quotes “.
The form a … b represents the set of characters from a through b as alternatives. The horizontal ellipsis … is also used elsewhere in the spec to informally denote various enumerations or code snippets that are not further specified.
QL source code representation ¶
QL source code is Unicode text encoded in UTF-8. The text is not canonicalized, so a single accented code point is distinct from the same character constructed from combining an accent and a letter; those are treated as two code points. For simplicity, this document will use the unqualified term character to refer to a Unicode code point in the source text.
Each code point is distinct; for instance, upper and lower case letters are different characters.
Implementation restriction: For compatibility with other tools, the parser may disallow the NUL character (U+0000) in the statement.
Implementation restriction: A byte order mark is disallowed anywhere in QL statements.
Characters ¶
The following terms are used to denote specific character classes
newline = . // the Unicode code point U+000A unicode_char = . // an arbitrary Unicode code point except newline ascii_letter = "a" … "z" | "A" … "Z" . unicode_letter = . // Unicode category L. unicode_digit = . // Unocode category D.
Letters and digits ¶
The underscore character _ (U+005F) is considered a letter.
letter = ascii_letter | unicode_letter | "_" . decimal_digit = "0" … "9" . octal_digit = "0" … "7" . hex_digit = "0" … "9" | "A" … "F" | "a" … "f" .
Lexical elements ¶
Lexical elements are comments, tokens, identifiers, keywords, operators and delimiters, integer, floating-point, imaginary, rune and string literals and QL parameters.
Comments ¶
There are three forms of comments ¶
Line comments start with the character sequence // or -- and stop at the end of the line. A line comment acts like a space.
General comments start with the character sequence /* and continue through the character sequence */. A general comment acts like a space.
Comments do not nest.
Tokens ¶
Tokens form the vocabulary of QL. There are four classes: identifiers, keywords, operators and delimiters, and literals. White space, formed from spaces (U+0020), horizontal tabs (U+0009), carriage returns (U+000D), and newlines (U+000A), is ignored except as it separates tokens that would otherwise combine into a single token.
Semicolons ¶
The formal grammar uses semicolons ";" as separators of QL statements. A single QL statement or the last QL statement in a list of statements can have an optional semicolon terminator. (Actually a separator from the following empty statement.)
Identifiers ¶
Identifiers name entities such as tables or record set columns. There are two kinds of identifiers, normal idententifiers and quoted identifiers.
indentifier = normal_identifier | quoted_identifier.
An normal identifier is a sequence of one or more letters and digits. The first character in an identifier must be a letter.
normal_identifier = letter { letter | decimal_digit | unicode_digit } .
For example
price _tmp42 Sales
A quoted identifier is a string of any charaters between guillmets «». Quoted identifiers allow QL key words or phrases with spaces to be used as identifiers. The guillemets were chosen because QL already uses double quotes, single quotes, and backticks for other quoting purposes.
quoted_identifier = "«" { unicode_char | newline } "»".
For example ¶
«TRANSACTION» «duration» «lovely stories»
No identifiers are predeclared, however note that no keyword can be used as a normal identifier. Identifiers starting with two underscores are used for meta data virtual tables names. For forward compatibility, users should generally avoid using any identifiers starting with two underscores. For example
__Column __Column2 __Index __Table
Keywords ¶
The following keywords are reserved and may not be used as identifiers.
ADD complex128 FROM LEFT string ALTER complex64 FULL LIKE TABLE AND CREATE GROUP LIMIT time AS DEFAULT IF NOT TRANSACTION ASC DELETE IN NULL true BEGIN DESC INDEX OFFSET TRUNCATE BETWEEN DISTINCT INSERT ON uint bigint DROP int OR uint16 bigrat duration int16 ORDER uint32 blob EXISTS int32 OUTER uint64 bool EXPLAIN int64 RIGHT uint8 BY false int8 ROLLBACK UNIQUE byte float INTO rune UPDATE COLUMN float32 IS SELECT VALUES COMMIT float64 JOIN SET WHERE
Keywords are not case sensitive.
Operators and Delimiters ¶
The following character sequences represent operators, delimiters, and other special tokens
- & && == != ( )
- | || < <= [ ]
- ^ > >= , ; / << = . % >> ! &^
Operators consisting of more than one character are referred to by names in the rest of the documentation
andand = "&&" . andnot = "&^" . lsh = "<<" . le = "<=" . eq = "==" | "=" . ge = ">=" . neq = "!=" . oror = "||" . rsh = ">>" .
Integer literals ¶
An integer literal is a sequence of digits representing an integer constant. An optional prefix sets a non-decimal base: 0 for octal, 0x or 0X for hexadecimal. In hexadecimal literals, letters a-f and A-F represent values 10 through 15.
int_lit = decimal_lit | octal_lit | hex_lit .
decimal_lit = ( "1" … "9" ) { decimal_digit } .
octal_lit = "0" { octal_digit } .
hex_lit = "0" ( "x" | "X" ) hex_digit { hex_digit } .
For example
42 0600 0xBadFace 1701411834604692
Floating-point literals ¶
A floating-point literal is a decimal representation of a floating-point constant. It has an integer part, a decimal point, a fractional part, and an exponent part. The integer and fractional part comprise decimal digits; the exponent part is an e or E followed by an optionally signed decimal exponent. One of the integer part or the fractional part may be elided; one of the decimal point or the exponent may be elided.
float_lit = decimals "." [ decimals ] [ exponent ] |
decimals exponent |
"." decimals [ exponent ] .
decimals = decimal_digit { decimal_digit } .
exponent = ( "e" | "E" ) [ "+" | "-" ] decimals .
For example
0. 72.40 072.40 // == 72.40 2.71828 1.e+0 6.67428e-11 1E6 .25 .12345E+5
Imaginary literals ¶
An imaginary literal is a decimal representation of the imaginary part of a complex constant. It consists of a floating-point literal or decimal integer followed by the lower-case letter i.
imaginary_lit = (decimals | float_lit) "i" .
For example
0i 011i // == 11i 0.i 2.71828i 1.e+0i 6.67428e-11i 1E6i .25i .12345E+5i
Rune literals ¶
A rune literal represents a rune constant, an integer value identifying a Unicode code point. A rune literal is expressed as one or more characters enclosed in single quotes. Within the quotes, any character may appear except single quote and newline. A single quoted character represents the Unicode value of the character itself, while multi-character sequences beginning with a backslash encode values in various formats.
The simplest form represents the single character within the quotes; since QL statements are Unicode characters encoded in UTF-8, multiple UTF-8-encoded bytes may represent a single integer value. For instance, the literal 'a' holds a single byte representing a literal a, Unicode U+0061, value 0x61, while 'ä' holds two bytes (0xc3 0xa4) representing a literal a-dieresis, U+00E4, value 0xe4.
Several backslash escapes allow arbitrary values to be encoded as ASCII text. There are four ways to represent the integer value as a numeric constant: \x followed by exactly two hexadecimal digits; \u followed by exactly four hexadecimal digits; \U followed by exactly eight hexadecimal digits, and a plain backslash \ followed by exactly three octal digits. In each case the value of the literal is the value represented by the digits in the corresponding base.
Although these representations all result in an integer, they have different valid ranges. Octal escapes must represent a value between 0 and 255 inclusive. Hexadecimal escapes satisfy this condition by construction. The escapes \u and \U represent Unicode code points so within them some values are illegal, in particular those above 0x10FFFF and surrogate halves.
After a backslash, certain single-character escapes represent special values
\a U+0007 alert or bell \b U+0008 backspace \f U+000C form feed \n U+000A line feed or newline \r U+000D carriage return \t U+0009 horizontal tab \v U+000b vertical tab \\ U+005c backslash \' U+0027 single quote (valid escape only within rune literals) \" U+0022 double quote (valid escape only within string literals)
All other sequences starting with a backslash are illegal inside rune literals.
rune_lit = "'" ( unicode_value | byte_value ) "'" .
unicode_value = unicode_char | little_u_value | big_u_value | escaped_char .
byte_value = octal_byte_value | hex_byte_value .
octal_byte_value = `\` octal_digit octal_digit octal_digit .
hex_byte_value = `\` "x" hex_digit hex_digit .
little_u_value = `\` "u" hex_digit hex_digit hex_digit hex_digit .
big_u_value = `\` "U" hex_digit hex_digit hex_digit hex_digit
hex_digit hex_digit hex_digit hex_digit .
escaped_char = `\` ( "a" | "b" | "f" | "n" | "r" | "t" | "v" | `\` | "'" | `"` ) .
For example
'a' 'ä' '本' '\t' '\000' '\007' '\377' '\x07' '\xff' '\u12e4' '\U00101234' 'aa' // illegal: too many characters '\xa' // illegal: too few hexadecimal digits '\0' // illegal: too few octal digits '\uDFFF' // illegal: surrogate half '\U00110000' // illegal: invalid Unicode code point
String literals ¶
A string literal represents a string constant obtained from concatenating a sequence of characters. There are two forms: raw string literals and interpreted string literals.
Raw string literals are character sequences between back quotes “. Within the quotes, any character is legal except back quote. The value of a raw string literal is the string composed of the uninterpreted (implicitly UTF-8-encoded) characters between the quotes; in particular, backslashes have no special meaning and the string may contain newlines. Carriage returns inside raw string literals are discarded from the raw string value.
Interpreted string literals are character sequences between double quotes "". The text between the quotes, which may not contain newlines, forms the value of the literal, with backslash escapes interpreted as they are in rune literals (except that \' is illegal and \" is legal), with the same restrictions. The three-digit octal (\nnn) and two-digit hexadecimal (\xnn) escapes represent individual bytes of the resulting string; all other escapes represent the (possibly multi-byte) UTF-8 encoding of individual characters. Thus inside a string literal \377 and \xFF represent a single byte of value 0xFF=255, while ÿ, \u00FF, \U000000FF and \xc3\xbf represent the two bytes 0xc3 0xbf of the UTF-8 encoding of character U+00FF.
string_lit = raw_string_lit | interpreted_string_lit .
raw_string_lit = "`" { unicode_char | newline } "`" .
interpreted_string_lit = `"` { unicode_value | byte_value } `"` .
For example
`abc` // same as "abc" `\n \n` // same as "\\n\n\\n" "\n" "" "Hello, world!\n" "日本語" "\u65e5本\U00008a9e" "\xff\u00FF" "\uD800" // illegal: surrogate half "\U00110000" // illegal: invalid Unicode code point
These examples all represent the same string
"日本語" // UTF-8 input text `日本語` // UTF-8 input text as a raw literal "\u65e5\u672c\u8a9e" // the explicit Unicode code points "\U000065e5\U0000672c\U00008a9e" // the explicit Unicode code points "\xe6\x97\xa5\xe6\x9c\xac\xe8\xaa\x9e" // the explicit UTF-8 bytes
If the statement source represents a character as two code points, such as a combining form involving an accent and a letter, the result will be an error if placed in a rune literal (it is not a single code point), and will appear as two code points if placed in a string literal.
QL parameters ¶
Literals are assigned their values from the respective text representation at "compile" (parse) time. QL parameters provide the same functionality as literals, but their value is assigned at execution time from an expression list passed to DB.Run or DB.Execute. Using '?' or '$' is completely equivalent.
ql_parameter = ( "?" | "$" ) "1" … "9" { "0" … "9" } .
For example
SELECT DepartmentID FROM department WHERE DepartmentID == ?1 ORDER BY DepartmentName; SELECT employee.LastName FROM department, employee WHERE department.DepartmentID == $1 && employee.LastName > $2 ORDER BY DepartmentID;
Constants ¶
Keywords 'false' and 'true' (not case sensitive) represent the two possible constant values of type bool (also not case sensitive).
Keyword 'NULL' (not case sensitive) represents an untyped constant which is assignable to any type. NULL is distinct from any other value of any type.
Types ¶
A type determines the set of values and operations specific to values of that type. A type is specified by a type name.
Type = "bigint" // http://golang.org/pkg/math/big/#Int
| "bigrat" // http://golang.org/pkg/math/big/#Rat
| "blob" // []byte
| "bool"
| "byte" // alias for uint8
| "complex128"
| "complex64"
| "duration" // http://golang.org/pkg/time/#Duration
| "float" // alias for float64
| "float32"
| "float64"
| "int" // alias for int64
| "int16"
| "int32"
| "int64"
| "int8"
| "rune" // alias for int32
| "string"
| "time" // http://golang.org/pkg/time/#Time
| "uint" // alias for uint64
| "uint16"
| "uint32"
| "uint64"
| "uint8" .
Named instances of the boolean, numeric, and string types are keywords. The names are not case sensitive.
Note: The blob type is exchanged between the back end and the API as []byte. On 32 bit platforms this limits the size which the implementation can handle to 2G.
Boolean types ¶
A boolean type represents the set of Boolean truth values denoted by the predeclared constants true and false. The predeclared boolean type is bool.
Duration type ¶
A duration type represents the elapsed time between two instants as an int64 nanosecond count. The representation limits the largest representable duration to approximately 290 years.
Numeric types ¶
A numeric type represents sets of integer or floating-point values. The predeclared architecture-independent numeric types are
uint8 the set of all unsigned 8-bit integers (0 to 255) uint16 the set of all unsigned 16-bit integers (0 to 65535) uint32 the set of all unsigned 32-bit integers (0 to 4294967295) uint64 the set of all unsigned 64-bit integers (0 to 18446744073709551615) int8 the set of all signed 8-bit integers (-128 to 127) int16 the set of all signed 16-bit integers (-32768 to 32767) int32 the set of all signed 32-bit integers (-2147483648 to 2147483647) int64 the set of all signed 64-bit integers (-9223372036854775808 to 9223372036854775807) duration the set of all signed 64-bit integers (-9223372036854775808 to 9223372036854775807) bigint the set of all integers bigrat the set of all rational numbers float32 the set of all IEEE-754 32-bit floating-point numbers float64 the set of all IEEE-754 64-bit floating-point numbers complex64 the set of all complex numbers with float32 real and imaginary parts complex128 the set of all complex numbers with float64 real and imaginary parts byte alias for uint8 float alias for float64 int alias for int64 rune alias for int32 uint alias for uint64
The value of an n-bit integer is n bits wide and represented using two's complement arithmetic.
Conversions are required when different numeric types are mixed in an expression or assignment.
String types ¶
A string type represents the set of string values. A string value is a (possibly empty) sequence of bytes. The case insensitive keyword for the string type is 'string'.
The length of a string (its size in bytes) can be discovered using the built-in function len.
Time types ¶
A time type represents an instant in time with nanosecond precision. Each time has associated with it a location, consulted when computing the presentation form of the time.
Predeclared functions ¶
The following functions are implicitly declared
avg complex contains count date day formatTime formatFloat formatInt hasPrefix hasSuffix hour hours id imag len max min minute minutes month nanosecond nanoseconds now parseTime real second seconds since sum timeIn weekday year yearDay
Expressions ¶
An expression specifies the computation of a value by applying operators and functions to operands.
Operands ¶
Operands denote the elementary values in an expression. An operand may be a literal, a (possibly qualified) identifier denoting a constant or a function or a table/record set column, or a parenthesized expression.
Operand = Literal | QualifiedIdent | "(" Expression ")" .
Literal = "FALSE" | "NULL" | "TRUE"
| float_lit | imaginary_lit | int_lit | rune_lit | string_lit
| ql_parameter .
Qualified identifiers ¶
A qualified identifier is an identifier qualified with a table/record set name prefix.
QualifiedIdent = identifier [ "." identifier ] .
For example
invoice.Num // might denote column 'Num' from table 'invoice'
Primary expressions ¶
Primary expression are the operands for unary and binary expressions.
PrimaryExpression = Operand
| Conversion
| PrimaryExpression Index
| PrimaryExpression Slice
| PrimaryExpression Call .
Call = "(" [ "*" | ExpressionList ] ")" . // * only in count(*).
Index = "[" Expression "]" .
Slice = "[" [ Expression ] ":" [ Expression ] "]" .
For example
x 2 (s + ".txt") f(3.1415, true) s[i : j + 1]
Index expressions ¶
A primary expression of the form
s[x]
denotes the element of a string indexed by x. Its type is byte. The value x is called the index. The following rules apply
- The index x must be of integer type except bigint or duration; it is in range if 0 <= x < len(s), otherwise it is out of range.
- A constant index must be non-negative and representable by a value of type int.
- A constant index must be in range if the string a is a literal.
- If x is out of range at run time, a run-time error occurs.
- s[x] is the byte at index x and the type of s[x] is byte.
If s is NULL or x is NULL then the result is NULL.
Otherwise s[x] is illegal.
Slices ¶
For a string, the primary expression
s[low : high]
constructs a substring. The indices low and high select which elements appear in the result. The result has indices starting at 0 and length equal to high - low.
For convenience, any of the indices may be omitted. A missing low index defaults to zero; a missing high index defaults to the length of the sliced operand
s[2:] // same s[2 : len(s)] s[:3] // same as s[0 : 3] s[:] // same as s[0 : len(s)]
The indices low and high are in range if 0 <= low <= high <= len(a), otherwise they are out of range. A constant index must be non-negative and representable by a value of type int. If both indices are constant, they must satisfy low <= high. If the indices are out of range at run time, a run-time error occurs.
Integer values of type bigint or duration cannot be used as indices.
If s is NULL the result is NULL. If low or high is not omitted and is NULL then the result is NULL.
Calls ¶
Given an identifier f denoting a predeclared function,
f(a1, a2, … an)
calls f with arguments a1, a2, … an. Arguments are evaluated before the function is called. The type of the expression is the result type of f.
complex(x, y) len(name)
In a function call, the function value and arguments are evaluated in the usual order. After they are evaluated, the parameters of the call are passed by value to the function and the called function begins execution. The return value of the function is passed by value when the function returns.
Calling an undefined function causes a compile-time error.
Operators ¶
Operators combine operands into expressions.
Expression = Term { ( oror | "OR" ) Term } .
ExpressionList = Expression { "," Expression } [ "," ].
Factor = PrimaryFactor { ( ge | ">" | le | "<" | neq | eq | "LIKE" ) PrimaryFactor } [ Predicate ] .
PrimaryFactor = PrimaryTerm { ( "^" | "|" | "-" | "+" ) PrimaryTerm } .
PrimaryTerm = UnaryExpr { ( andnot | "&" | lsh | rsh | "%" | "/" | "*" ) UnaryExpr } .
Term = Factor { ( andand | "AND" ) Factor } .
UnaryExpr = [ "^" | "!" | "-" | "+" ] PrimaryExpression .
Comparisons are discussed elsewhere. For other binary operators, the operand types must be identical unless the operation involves shifts or untyped constants. For operations involving constants only, see the section on constant expressions.
Except for shift operations, if one operand is an untyped constant and the other operand is not, the constant is converted to the type of the other operand.
The right operand in a shift expression must have unsigned integer type or be an untyped constant that can be converted to unsigned integer type. If the left operand of a non-constant shift expression is an untyped constant, the type of the constant is what it would be if the shift expression were replaced by its left operand alone.
Pattern matching ¶
Expressions of the form
expr1 LIKE expr2
yield a boolean value true if expr2, a regular expression, matches expr1 (see also [6]). Both expression must be of type string. If any one of the expressions is NULL the result is NULL.
Predicates ¶
Predicates are special form expressions having a boolean result type.
Expressions of the form
expr IN ( expr1, expr2, expr3, ... ) // case A expr NOT IN ( expr1, expr2, expr3, ... ) // case B
are equivalent, including NULL handling, to
expr == expr1 || expr == expr2 || expr == expr3 || ... // case A expr != expr1 && expr != expr2 && expr != expr3 && ... // case B
The types of involved expressions must be comparable as defined in "Comparison operators".
Another form of the IN predicate creates the expression list from a result of a SelectStmt.
DELETE FROM t WHERE id() IN (SELECT id_t FROM u WHERE inactive_days > 365)
The SelectStmt must select only one column. The produced expression list is resource limited by the memory available to the process. NULL values produced by the SelectStmt are ignored, but if all records of the SelectStmt are NULL the predicate yields NULL. The select statement is evaluated only once. If the type of expr is not the same as the type of the field returned by the SelectStmt then the set operation yields false. The type of the column returned by the SelectStmt must be one of the simple (non blob-like) types:
bool byte // alias uint8 complex128 complex64 float // alias float64 float32 float64 int // alias int64 int16 int32 int64 int8 rune // alias int32 string uint // alias uint64 uint16 uint32 uint64 uint8
Expressions of the form
expr BETWEEN low AND high // case A expr NOT BETWEEN low AND high // case B
are equivalent, including NULL handling, to
expr >= low && expr <= high // case A expr < low || expr > high // case B
The types of involved expressions must be ordered as defined in "Comparison operators".
Predicate = (
[ "NOT" ] (
"IN" "(" ExpressionList ")"
| "IN" "(" SelectStmt [ ";" ] ")"
| "BETWEEN" PrimaryFactor "AND" PrimaryFactor
)
| "IS" [ "NOT" ] "NULL"
).
Expressions of the form
expr IS NULL // case A expr IS NOT NULL // case B
yield a boolean value true if expr does not have a specific type (case A) or if expr has a specific type (case B). In other cases the result is a boolean value false.
Operator precedence ¶
Unary operators have the highest precedence.
There are five precedence levels for binary operators. Multiplication operators bind strongest, followed by addition operators, comparison operators, && (logical AND), and finally || (logical OR)
Precedence Operator
5 * / % << >> & &^
4 + - | ^
3 == != < <= > >=
2 &&
1 ||
Binary operators of the same precedence associate from left to right. For instance, x / y * z is the same as (x / y) * z.
+x 23 + 3*x[i] x <= f() ^a >> b f() || g() x == y+1 && z > 0
Note that the operator precedence is reflected explicitly by the grammar.
Arithmetic operators ¶
Arithmetic operators apply to numeric values and yield a result of the same type as the first operand. The four standard arithmetic operators (+, -, *, /) apply to integer, rational, floating-point, and complex types; + also applies to strings; +,- also applies to times. All other arithmetic operators apply to integers only.
sum integers, rationals, floats, complex values, strings
difference integers, rationals, floats, complex values, times
product integers, rationals, floats, complex values / quotient integers, rationals, floats, complex values % remainder integers
& bitwise AND integers | bitwise OR integers ^ bitwise XOR integers &^ bit clear (AND NOT) integers
<< left shift integer << unsigned integer >> right shift integer >> unsigned integer
Strings can be concatenated using the + operator
"hi" + string(c) + " and good bye"
String addition creates a new string by concatenating the operands.
A value of type duration can be added to or subtracted from a value of type time.
now() + duration("1h") // time after 1 hour from now
duration("1h") + now() // time after 1 hour from now
now() - duration("1h") // time before 1 hour from now
duration("1h") - now() // illegal, negative times do not exist
Times can subtracted from each other producing a value of type duration.
now() - t0 // elapsed time since t0 now() + now() // illegal, operator + not defined for times
For two integer values x and y, the integer quotient q = x / y and remainder r = x % y satisfy the following relationships
x = q*y + r and |r| < |y|
with x / y truncated towards zero ("truncated division").
x y x / y x % y 5 3 1 2 -5 3 -1 -2 5 -3 -1 2 -5 -3 1 -2
As an exception to this rule, if the dividend x is the most negative value for the int type of x, the quotient q = x / -1 is equal to x (and r = 0).
x, q int8 -128 int16 -32768 int32 -2147483648 int64 -9223372036854775808
If the divisor is a constant expression, it must not be zero. If the divisor is zero at run time, a run-time error occurs. If the dividend is non-negative and the divisor is a constant power of 2, the division may be replaced by a right shift, and computing the remainder may be replaced by a bitwise AND operation
x x / 4 x % 4 x >> 2 x & 3 11 2 3 2 3 -11 -2 -3 -3 1
The shift operators shift the left operand by the shift count specified by the right operand. They implement arithmetic shifts if the left operand is a signed integer and logical shifts if it is an unsigned integer. There is no upper limit on the shift count. Shifts behave as if the left operand is shifted n times by 1 for a shift count of n. As a result, x << 1 is the same as x*2 and x >> 1 is the same as x/2 but truncated towards negative infinity.
For integer operands, the unary operators +, -, and ^ are defined as follows
+x is 0 + x
-x negation is 0 - x
^x bitwise complement is m ^ x with m = "all bits set to 1" for unsigned x
and m = -1 for signed x
For floating-point and complex numbers, +x is the same as x, while -x is the negation of x. The result of a floating-point or complex division by zero is not specified beyond the IEEE-754 standard; whether a run-time error occurs is implementation-specific.
Whenever any operand of any arithmetic operation, unary or binary, is NULL, as well as in the case of the string concatenating operation, the result is NULL.
42*NULL // the result is NULL NULL/x // the result is NULL "foo"+NULL // the result is NULL
Integer overflow ¶
For unsigned integer values, the operations +, -, *, and << are computed modulo 2n, where n is the bit width of the unsigned integer's type. Loosely speaking, these unsigned integer operations discard high bits upon overflow, and expressions may rely on “wrap around”.
For signed integers with a finite bit width, the operations +, -, *, and << may legally overflow and the resulting value exists and is deterministically defined by the signed integer representation, the operation, and its operands. No exception is raised as a result of overflow. An evaluator may not optimize an expression under the assumption that overflow does not occur. For instance, it may not assume that x < x + 1 is always true.
Integers of type bigint and rationals do not overflow but their handling is limited by the memory resources available to the program.
Comparison operators ¶
Comparison operators compare two operands and yield a boolean value.
== equal != not equal < less <= less or equal > greater >= greater or equal
In any comparison, the first operand must be of same type as is the second operand, or vice versa.
The equality operators == and != apply to operands that are comparable. The ordering operators <, <=, >, and >= apply to operands that are ordered. These terms and the result of the comparisons are defined as follows
- Boolean values are comparable. Two boolean values are equal if they are either both true or both false.
- Complex values are comparable. Two complex values u and v are equal if both real(u) == real(v) and imag(u) == imag(v).
- Integer values are comparable and ordered, in the usual way. Note that durations are integers.
- Floating point values are comparable and ordered, as defined by the IEEE-754 standard.
- Rational values are comparable and ordered, in the usual way.
- String and Blob values are comparable and ordered, lexically byte-wise.
- Time values are comparable and ordered.
Whenever any operand of any comparison operation is NULL, the result is NULL.
Note that slices are always of type string.
Logical operators ¶
Logical operators apply to boolean values and yield a boolean result. The right operand is evaluated conditionally.
&& conditional AND p && q is "if p then q else false" || conditional OR p || q is "if p then true else q" ! NOT !p is "not p"
The truth tables for logical operations with NULL values
+-------+-------+---------+---------+ | p | q | p || q | p && q | +-------+-------+---------+---------+ | true | true | *true | true | | true | false | *true | false | | true | NULL | *true | NULL | | false | true | true | *false | | false | false | false | *false | | false | NULL | NULL | *false | | NULL | true | true | NULL | | NULL | false | NULL | false | | NULL | NULL | NULL | NULL | +-------+-------+---------+---------+ * indicates q is not evaluated. +-------+-------+ | p | !p | +-------+-------+ | true | false | | false | true | | NULL | NULL | +-------+-------+
Conversions ¶
Conversions are expressions of the form T(x) where T is a type and x is an expression that can be converted to type T.
Conversion = Type "(" Expression ")" .
A constant value x can be converted to type T in any of these cases:
- x is representable by a value of type T.
- x is a floating-point constant, T is a floating-point type, and x is representable by a value of type T after rounding using IEEE 754 round-to-even rules. The constant T(x) is the rounded value.
- x is an integer constant and T is a string type. The same rule as for non-constant x applies in this case.
Converting a constant yields a typed constant as result.
float32(2.718281828) // 2.718281828 of type float32
complex128(1) // 1.0 + 0.0i of type complex128
float32(0.49999999) // 0.5 of type float32
string('x') // "x" of type string
string(0x266c) // "♬" of type string
"foo" + "bar" // "foobar"
int(1.2) // illegal: 1.2 cannot be represented as an int
string(65.0) // illegal: 65.0 is not an integer constant
A non-constant value x can be converted to type T in any of these cases:
- x has type T.
- x's type and T are both integer or floating point types.
- x's type and T are both complex types.
- x is an integer, except bigint or duration, and T is a string type.
Specific rules apply to (non-constant) conversions between numeric types or to and from a string type. These conversions may change the representation of x and incur a run-time cost. All other conversions only change the type but not the representation of x.
A conversion of NULL to any type yields NULL.
Conversions between numeric types ¶
For the conversion of non-constant numeric values, the following rules apply
1. When converting between integer types, if the value is a signed integer, it is sign extended to implicit infinite precision; otherwise it is zero extended. It is then truncated to fit in the result type's size. For example, if v == uint16(0x10F0), then uint32(int8(v)) == 0xFFFFFFF0. The conversion always yields a valid value; there is no indication of overflow.
2. When converting a floating-point number to an integer, the fraction is discarded (truncation towards zero).
3. When converting an integer or floating-point number to a floating-point type, or a complex number to another complex type, the result value is rounded to the precision specified by the destination type. For instance, the value of a variable x of type float32 may be stored using additional precision beyond that of an IEEE-754 32-bit number, but float32(x) represents the result of rounding x's value to 32-bit precision. Similarly, x + 0.1 may use more than 32 bits of precision, but float32(x + 0.1) does not.
In all non-constant conversions involving floating-point or complex values, if the result type cannot represent the value the conversion succeeds but the result value is implementation-dependent.
Conversions to and from a string type ¶
1. Converting a signed or unsigned integer value to a string type yields a string containing the UTF-8 representation of the integer. Values outside the range of valid Unicode code points are converted to "\uFFFD".
string('a') // "a"
string(-1) // "\ufffd" == "\xef\xbf\xbd"
string(0xf8) // "\u00f8" == "ø" == "\xc3\xb8"
string(0x65e5) // "\u65e5" == "日" == "\xe6\x97\xa5"
2. Converting a blob to a string type yields a string whose successive bytes are the elements of the blob.
string(b /* []byte{'h', 'e', 'l', 'l', '\xc3', '\xb8'} */) // "hellø"
string(b /* []byte{} */) // ""
string(b /* []byte(nil) */) // ""
3. Converting a value of a string type to a blob yields a blob whose successive elements are the bytes of the string.
blob("hellø") // []byte{'h', 'e', 'l', 'l', '\xc3', '\xb8'}
blob("") // []byte{}
4. Converting a value of a bigint type to a string yields a string containing the decimal decimal representation of the integer.
string(M9) // "2305843009213693951"
5. Converting a value of a string type to a bigint yields a bigint value containing the integer represented by the string value. A prefix of “0x” or “0X” selects base 16; the “0” prefix selects base 8, and a “0b” or “0B” prefix selects base 2. Otherwise the value is interpreted in base 10. An error occurs if the string value is not in any valid format.
bigint("2305843009213693951") // M9
bigint("0x1ffffffffffffffffffffff") // M10 == 2^89-1
6. Converting a value of a rational type to a string yields a string containing the decimal decimal representation of the rational in the form "a/b" (even if b == 1).
string(bigrat(355)/bigrat(113)) // "355/113"
7. Converting a value of a string type to a bigrat yields a bigrat value containing the rational represented by the string value. The string can be given as a fraction "a/b" or as a floating-point number optionally followed by an exponent. An error occurs if the string value is not in any valid format.
bigrat("1.2e-34")
bigrat("355/113")
8. Converting a value of a duration type to a string returns a string representing the duration in the form "72h3m0.5s". Leading zero units are omitted. As a special case, durations less than one second format using a smaller unit (milli-, micro-, or nanoseconds) to ensure that the leading digit is non-zero. The zero duration formats as 0, with no unit.
string(elapsed) // "1h", for example
9. Converting a string value to a duration yields a duration represented by the string. A duration string is a possibly signed sequence of decimal numbers, each with optional fraction and a unit suffix, such as "300ms", "-1.5h" or "2h45m". Valid time units are "ns", "us" (or "µs"), "ms", "s", "m", "h".
duration("1m") // http://golang.org/pkg/time/#Minute
10. Converting a time value to a string returns the time formatted using the format string
"2006-01-02 15:04:05.999999999 -0700 MST"
Order of evaluation ¶
When evaluating the operands of an expression or of function calls, operations are evaluated in lexical left-to-right order.
For example, in the evaluation of
g(h(), i()+x[j()], c)
the function calls and evaluation of c happen in the order h(), i(), j(), c.
Floating-point operations within a single expression are evaluated according to the associativity of the operators. Explicit parentheses affect the evaluation by overriding the default associativity. In the expression x + (y + z) the addition y + z is performed before adding x.
Statements ¶
Statements control execution.
Statement = EmptyStmt | AlterTableStmt | BeginTransactionStmt | CommitStmt
| CreateIndexStmt | CreateTableStmt | DeleteFromStmt | DropIndexStmt
| DropTableStmt | InsertIntoStmt | RollbackStmt | SelectStmt
| TruncateTableStmt | UpdateStmt | ExplainStmt.
StatementList = Statement { ";" Statement } .
Empty statements ¶
The empty statement does nothing.
EmptyStmt = .
ALTER TABLE ¶
Alter table statements modify existing tables. With the ADD clause it adds a new column to the table. The column must not exist. With the DROP clause it removes an existing column from a table. The column must exist and it must be not the only (last) column of the table. IOW, there cannot be a table with no columns.
AlterTableStmt = "ALTER" "TABLE" TableName ( "ADD" ColumnDef | "DROP" "COLUMN" ColumnName ) .
For example
BEGIN TRANSACTION; ALTER TABLE Stock ADD Qty int; ALTER TABLE Income DROP COLUMN Taxes; COMMIT;
When adding a column to a table with existing data, the constraint clause of the ColumnDef cannot be used. Adding a constrained column to an empty table is fine.
BEGIN TRANSACTION ¶
Begin transactions statements introduce a new transaction level. Every transaction level must be eventually balanced by exactly one of COMMIT or ROLLBACK statements. Note that when a transaction is roll-backed because of a statement failure then no explicit balancing of the respective BEGIN TRANSACTION is statement is required nor permitted.
Failure to properly balance any opened transaction level may cause dead locks and/or lose of data updated in the uppermost opened but never properly closed transaction level.
BeginTransactionStmt = "BEGIN" "TRANSACTION" .
For example
BEGIN TRANSACTION; INSERT INTO foo VALUES (42, 3.14); INSERT INTO foo VALUES (-1, 2.78); COMMIT;
Mandatory transactions ¶
A database cannot be updated (mutated) outside of a transaction. Statements requiring a transaction
ALTER TABLE COMMIT CREATE INDEX CREATE TABLE DELETE FROM DROP INDEX DROP TABLE INSERT INTO ROLLBACK TRUNCATE TABLE UPDATE
A database is effectively read only outside of a transaction. Statements not requiring a transaction
BEGIN TRANSACTION SELECT FROM
COMMIT ¶
The commit statement closes the innermost transaction nesting level. If that's the outermost level then the updates to the DB made by the transaction are atomically made persistent.
CommitStmt = "COMMIT" .
For example
BEGIN TRANSACTION; INSERT INTO AccountA (Amount) VALUES ($1); INSERT INTO AccountB (Amount) VALUES (-$1); COMMIT;
CREATE INDEX ¶
Create index statements create new indices. Index is a named projection of ordered values of a table column to the respective records. As a special case the id() of the record can be indexed. Index name must not be the same as any of the existing tables and it also cannot be the same as of any column name of the table the index is on.
CreateIndexStmt = "CREATE" [ "UNIQUE" ] "INDEX" [ "IF" "NOT" "EXISTS" ]
IndexName "ON" TableName "(" ExpressionList ")" .
For example
BEGIN TRANSACTION; CREATE TABLE Orders (CustomerID int, Date time); CREATE INDEX OrdersID ON Orders (id()); CREATE INDEX OrdersDate ON Orders (Date); CREATE TABLE Items (OrderID int, ProductID int, Qty int); CREATE INDEX ItemsOrderID ON Items (OrderID); COMMIT;
Now certain SELECT statements may use the indices to speed up joins and/or to speed up record set filtering when the WHERE clause is used; or the indices might be used to improve the performance when the ORDER BY clause is present.
The UNIQUE modifier requires the indexed values tuple to be index-wise unique or have all values NULL.
The optional IF NOT EXISTS clause makes the statement a no operation if the index already exists.
Simple index ¶
A simple index consists of only one expression which must be either a column name or the built-in id().
Expression list index ¶
A more complex and more general index is one that consists of more than one expression or its single expression does not qualify as a simple index. In this case the type of all expressions in the list must be one of the non blob-like types.
Note: Blob-like types are blob, bigint, bigrat, time and duration.
CREATE TABLE ¶
Create table statements create new tables. A column definition declares the column name and type. Table names and column names are case sensitive. Neither a table or an index of the same name may exist in the DB.
CreateTableStmt = "CREATE" "TABLE" [ "IF" "NOT" "EXISTS" ] TableName
"(" ColumnDef { "," ColumnDef } [ "," ] ")" .
ColumnDef = ColumnName Type [ "NOT" "NULL" | Expression ] [ "DEFAULT" Expression ] .
ColumnName = identifier .
TableName = identifier .
For example
BEGIN TRANSACTION; CREATE TABLE department ( DepartmentID int, DepartmentName string, ); CREATE TABLE employee ( LastName string, DepartmentID int, ); COMMIT;
The optional IF NOT EXISTS clause makes the statement a no operation if the table already exists.
The optional constraint clause has two forms. The first one is found in many SQL dialects.
BEGIN TRANSACTION; CREATE TABLE department ( DepartmentID int, DepartmentName string NOT NULL, ); COMMIT;
This form prevents the data in column DepartmentName to be NULL.
The second form allows an arbitrary boolean expression to be used to validate the column. If the value of the expression is true then the validation succeeded. If the value of the expression is false or NULL then the validation fails. If the value of the expression is not of type bool an error occurs.
BEGIN TRANSACTION;
CREATE TABLE department (
DepartmentID int,
DepartmentName string DepartmentName IN ("HQ", "R/D", "Lab", "HR"),
);
COMMIT;
BEGIN TRANSACTION;
CREATE TABLE t (
TimeStamp time TimeStamp < now() && since(TimeStamp) < duration("10s"),
Event string Event != "" && Event like "[0-9]+:[ \t]+.*",
);
COMMIT;
The optional DEFAULT clause is an expression which, if present, is substituted instead of a NULL value when the colum is assigned a value.
BEGIN TRANSACTION;
CREATE TABLE department (
DepartmentID int,
DepartmentName string DepartmentName IN ("HQ", "R/D", "Lab", "HR") DEFAULT "HQ",
);
COMMIT;
Note that the constraint and/or default expressions may refer to other columns by name:
BEGIN TRANSACTION; CREATE TABLE t ( a int, b int b > a && b < c DEFAULT (a+c)/2, c int, ); COMMIT;
Constraints and defaults ¶
When a table row is inserted by the INSERT INTO statement or when a table row is updated by the UPDATE statement, the order of operations is as follows:
1. The new values of the affected columns are set and the values of all the row columns become the named values which can be referred to in default expressions evaluated in step 2.
2. If any row column value is NULL and the DEFAULT clause is present in the column's definition, the default expression is evaluated and its value is set as the respective column value.
3. The values, potentially updated, of row columns become the named values which can be referred to in constraint expressions evaluated during step 4.
4. All row columns which definition has the constraint clause present will have that constraint checked. If any constraint violation is detected, the overall operation fails and no changes to the table are made.
DELETE FROM ¶
Delete from statements remove rows from a table, which must exist.
DeleteFromStmt = "DELETE" "FROM" TableName [ WhereClause ] .
For example
BEGIN TRANSACTION; DELETE FROM DepartmentID WHERE DepartmentName == "Ponies"; COMMIT;
If the WHERE clause is not present then all rows are removed and the statement is equivalent to the TRUNCATE TABLE statement.
DROP INDEX ¶
Drop index statements remove indices from the DB. The index must exist.
DropIndexStmt = "DROP" "INDEX" [ "IF" "EXISTS" ] IndexName . IndexName = identifier .
For example
BEGIN TRANSACTION; DROP INDEX ItemsOrderID; COMMIT;
The optional IF EXISTS clause makes the statement a no operation if the index does not exist.
DROP TABLE ¶
Drop table statements remove tables from the DB. The table must exist.
DropTableStmt = "DROP" "TABLE" [ "IF" "EXISTS" ] TableName .
For example
BEGIN TRANSACTION; DROP TABLE Inventory; COMMIT;
The optional IF EXISTS clause makes the statement a no operation if the table does not exist.
INSERT INTO ¶
Insert into statements insert new rows into tables. New rows come from literal data, if using the VALUES clause, or are a result of select statement. In the later case the select statement is fully evaluated before the insertion of any rows is performed, allowing to insert values calculated from the same table rows are to be inserted into. If the ColumnNameList part is omitted then the number of values inserted in the row must be the same as are columns in the table. If the ColumnNameList part is present then the number of values per row must be same as the same number of column names. All other columns of the record are set to NULL. The type of the value assigned to a column must be the same as is the column's type or the value must be NULL.
If there exists an unique index that would make the insert statement fail, the optional IF NOT EXISTS turns the insert statement in such case into a no-op.
InsertIntoStmt = "INSERT" "INTO" TableName [ "IF" "NOT" "EXISTS" ]
[ "(" ColumnNameList ")" ] ( Values | SelectStmt ) .
ColumnNameList = ColumnName { "," ColumnName } [ "," ] .
Values = "VALUES" "(" ExpressionList ")" { "," "(" ExpressionList ")" } [ "," ] .
For example
BEGIN TRANSACTION; INSERT INTO department (DepartmentID) VALUES (42); INSERT INTO department ( DepartmentName, DepartmentID, ) VALUES ( "R&D", 42, ); INSERT INTO department VALUES (42, "R&D"), (17, "Sales"), ; COMMIT; BEGIN TRANSACTION; INSERT INTO department (DepartmentName, DepartmentID) SELECT DepartmentName+"/headquarters", DepartmentID+1000 FROM department; COMMIT;
If any of the columns of the table were defined using the optional constraints clause or the optional defaults clause then those are processed on a per row basis. The details are discussed in the "Constraints and defaults" chapter below the CREATE TABLE statement documentation.
Explain statement ¶
Explain statement produces a recordset consisting of lines of text which describe the execution plan of a statement, if any.
ExplainStmt = "EXPLAIN" Statement .
For example, the QL tool treats the explain statement specially and outputs the joined lines:
$ ql 'create table t(i int); create table u(j int)' $ ql 'explain select * from t, u where t.i > 42 && u.j < 314' ┌Compute Cartesian product of │ ┌Iterate all rows of table "t" │ └Output field names ["i"] │ ┌Iterate all rows of table "u" │ └Output field names ["j"] └Output field names ["t.i" "u.j"] ┌Filter on t.i > 42 && u.j < 314 │Possibly useful indices │CREATE INDEX xt_i ON t(i); │CREATE INDEX xu_j ON u(j); └Output field names ["t.i" "u.j"] $ ql 'CREATE INDEX xt_i ON t(i); CREATE INDEX xu_j ON u(j);' $ ql 'explain select * from t, u where t.i > 42 && u.j < 314' ┌Compute Cartesian product of │ ┌Iterate all rows of table "t" using index "xt_i" where i > 42 │ └Output field names ["i"] │ ┌Iterate all rows of table "u" using index "xu_j" where j < 314 │ └Output field names ["j"] └Output field names ["t.i" "u.j"] $ ql 'explain select * from t where i > 12 and i between 10 and 20 and i < 42' ┌Iterate all rows of table "t" using index "xt_i" where i > 12 && i <= 20 └Output field names ["i"] $
The explanation may aid in uderstanding how a statement/query would be executed and if indices are used as expected - or which indices may possibly improve the statement performance. The create index statements above were directly copy/pasted in the terminal from the suggestions provided by the filter recordset pipeline part returned by the explain statement.
If the statement has nothing special in its plan, the result is the original statement.
$ ql 'explain delete from t where 42 < i' DELETE FROM t WHERE i > 42; $
To get an explanation of the select statement of the IN predicate, use the EXPLAIN statement with that particular select statement.
$ ql 'explain select * from t where i in (select j from u where j > 0)' ┌Iterate all rows of table "t" └Output field names ["i"] ┌Filter on i IN (SELECT j FROM u WHERE j > 0;) └Output field names ["i"] $ ql 'explain select j from u where j > 0' ┌Iterate all rows of table "u" using index "xu_j" where j > 0 └Output field names ["j"] $
ROLLBACK ¶
The rollback statement closes the innermost transaction nesting level discarding any updates to the DB made by it. If that's the outermost level then the effects on the DB are as if the transaction never happened.
RollbackStmt = "ROLLBACK" .
For example
// First statement list BEGIN TRANSACTION SELECT * INTO tmp FROM foo; INSERT INTO tmp SELECT * from bar; SELECT * from tmp;
The (temporary) record set from the last statement is returned and can be processed by the client.
// Second statement list ROLLBACK;
In this case the rollback is the same as 'DROP TABLE tmp;' but it can be a more complex operation.
SELECT FROM ¶
Select from statements produce recordsets. The optional DISTINCT modifier ensures all rows in the result recordset are unique. Either all of the resulting fields are returned ('*') or only those named in FieldList.
RecordSetList is a list of table names or parenthesized select statements, optionally (re)named using the AS clause.
The result can be filtered using a WhereClause and orderd by the OrderBy clause.
SelectStmt = "SELECT" [ "DISTINCT" ] ( "*" | FieldList ) [ "FROM" RecordSetList ]
[ JoinClause ] [ WhereClause ] [ GroupByClause ] [ OrderBy ] [ Limit ] [ Offset ].
JoinClause = ( "LEFT" | "RIGHT" | "FULL" ) [ "OUTER" ] "JOIN" RecordSet "ON" Expression .
RecordSet = ( TableName | "(" SelectStmt [ ";" ] ")" ) [ "AS" identifier ] .
RecordSetList = RecordSet { "," RecordSet } [ "," ] .
For example
SELECT * FROM Stock; SELECT DepartmentID FROM department WHERE DepartmentID == 42 ORDER BY DepartmentName; SELECT employee.LastName FROM department, employee WHERE department.DepartmentID == employee.DepartmentID ORDER BY DepartmentID;
If Recordset is a nested, parenthesized SelectStmt then it must be given a name using the AS clause if its field are to be accessible in expressions.
SELECT a.b, c.d FROM x AS a, ( SELECT * FROM y; ) AS c WHERE a.e > c.e;
Fields naming rules ¶
A field is an named expression. Identifiers, not used as a type in conversion or a function name in the Call clause, denote names of (other) fields, values of which should be used in the expression.
Field = Expression [ "AS" identifier ] .
The expression can be named using the AS clause. If the AS clause is not present and the expression consists solely of a field name, then that field name is used as the name of the resulting field. Otherwise the field is unnamed.
For example
SELECT 314, 42 as AUQLUE, DepartmentID, DepartmentID+1000, LastName as Name from employee;
// Fields are []string{"", "AUQLUE", "DepartmentID", "", "Name"}
The SELECT statement can optionally enumerate the desired/resulting fields in a list.
FieldList = Field { "," Field } [ "," ] .
No two identical field names can appear in the list.
SELECT DepartmentID, LastName, DepartmentID from employee; // duplicate field name "DepartmentID" SELECT DepartmentID, LastName, DepartmentID as ID2 from employee; // works
When more than one record set is used in the FROM clause record set list, the result record set field names are rewritten to be qualified using the record set names.
SELECT * FROM employee, department;
// Fields are []string{"employee.LastName", "employee.DepartmentID", "department.DepartmentID", "department.DepartmentName"
If a particular record set doesn't have a name, its respective fields became unnamed.
SELECT * FROM employee as e, ( SELECT * FROM department);
// Fields are []string{"e.LastName", "e.DepartmentID", "", ""
SELECT * FROM employee AS e, ( SELECT * FROM department) AS d;
// Fields are []string{"e.LastName", "e.DepartmentID", "d.DepartmentID", "d.DepartmentName"
Outer joins ¶
The optional JOIN clause, for example
SELECT * FROM a LEFT OUTER JOIN b ON expr;
is mostly equal to
SELECT * FROM a, b WHERE expr;
except that the rows from a which, when they appear in the cross join, never made expr to evaluate to true, are combined with a virtual row from b, containing all nulls, and added to the result set. For the RIGHT JOIN variant the discussed rules are used for rows from b not satisfying expr == true and the virtual, all-null row "comes" from a. The FULL JOIN adds the respective rows which would be otherwise provided by the separate executions of the LEFT JOIN and RIGHT JOIN variants. For more thorough OUTER JOIN discussion please see the Wikipedia article at [10].
Recordset ordering ¶
Resultins rows of a SELECT statement can be optionally ordered by the ORDER BY clause. Collating proceeds by considering the expressions in the expression list left to right until a collating order is determined. Any possibly remaining expressions are not evaluated.
OrderBy = "ORDER" "BY" ExpressionList [ "ASC" | "DESC" ] .
All of the expression values must yield an ordered type or NULL. Ordered types are defined in "Comparison operators". Collating of elements having a NULL value is different compared to what the comparison operators yield in expression evaluation (NULL result instead of a boolean value).
Below, T denotes a non NULL value of any QL type.
NULL < T
NULL collates before any non NULL value (is considered smaller than T).
NULL == NULL
Two NULLs have no collating order (are considered equal).
Recordset filtering ¶
The WHERE clause restricts records considered by some statements, like SELECT FROM, DELETE FROM, or UPDATE.
expression value consider the record ---------------- ------------------- true yes false or NULL no
It is an error if the expression evaluates to a non null value of non bool type.
Another form of the WHERE clause is an existence predicate of a parenthesized select statement. The EXISTS form evaluates to true if the parenthesized SELECT statement produces a non empty record set. The NOT EXISTS form evaluates to true if the parenthesized SELECT statement produces an empty record set. The parenthesized SELECT statement is evaluated only once (TODO issue #159).
WhereClause = "WHERE" Expression
| "WHERE" "EXISTS" "(" SelectStmt ")"
| "WHERE" "NOT" "EXISTS" "(" SelectStmt ")" .
Recordset grouping ¶
The GROUP BY clause is used to project rows having common values into a smaller set of rows.
For example
SELECT Country, sum(Qty) FROM Sales GROUP BY Country; SELECT Country, Product FROM Sales GROUP BY Country, Product; SELECT DISTINCT Country, Product FROM Sales;
Using the GROUP BY without any aggregate functions in the selected fields is in certain cases equal to using the DISTINCT modifier. The last two examples above produce the same resultsets.
GroupByClause = "GROUP BY" ColumnNameList .
Skipping records ¶
The optional OFFSET clause allows to ignore first N records. For example
SELECT * FROM t OFFSET 10;
The above will produce only rows 11, 12, ... of the record set, if they exist. The value of the expression must a non negative integer, but not bigint or duration.
Offset = "OFFSET" Expression .
Limiting the result set size ¶
The optional LIMIT clause allows to ignore all but first N records. For example
SELECT * FROM t LIMIT 10;
The above will return at most the first 10 records of the record set. The value of the expression must a non negative integer, but not bigint or duration.
Limit = "Limit" Expression .
The LIMIT and OFFSET clauses can be combined. For example
SELECT * FROM t LIMIT 5 OFFSET 3;
Considering table t has, say 10 records, the above will produce only records 4 - 8.
#1: Ignore 1/3 #2: Ignore 2/3 #3: Ignore 3/3 #4: Return 1/5 #5: Return 2/5 #6: Return 3/5 #7: Return 4/5 #8: Return 5/5
After returning record #8, no more result rows/records are computed.
Select statement evaluation order ¶
1. The FROM clause is evaluated, producing a Cartesian product of its source record sets (tables or nested SELECT statements).
2. If present, the JOIN cluase is evaluated on the result set of the previous evaluation and the recordset specified by the JOIN clause. (... JOIN Recordset ON ...)
3. If present, the WHERE clause is evaluated on the result set of the previous evaluation.
4. If present, the GROUP BY clause is evaluated on the result set of the previous evaluation(s).
5. The SELECT field expressions are evaluated on the result set of the previous evaluation(s).
6. If present, the DISTINCT modifier is evaluated on the result set of the previous evaluation(s).
7. If present, the ORDER BY clause is evaluated on the result set of the previous evaluation(s).
8. If present, the OFFSET clause is evaluated on the result set of the previous evaluation(s). The offset expression is evaluated once for the first record produced by the previous evaluations.
9. If present, the LIMIT clause is evaluated on the result set of the previous evaluation(s). The limit expression is evaluated once for the first record produced by the previous evaluations.
TRUNCATE TABLE ¶
Truncate table statements remove all records from a table. The table must exist.
TruncateTableStmt = "TRUNCATE" "TABLE" TableName .
For example
BEGIN TRANSACTION TRUNCATE TABLE department; COMMIT;
UPDATE ¶
Update statements change values of fields in rows of a table.
UpdateStmt = "UPDATE" TableName [ "SET" ] AssignmentList [ WhereClause ] .
AssignmentList = Assignment { "," Assignment } [ "," ] .
Assignment = ColumnName "=" Expression .
For example
BEGIN TRANSACTION UPDATE department DepartmentName = DepartmentName + " dpt.", DepartmentID = 1000+DepartmentID, WHERE DepartmentID < 1000; COMMIT;
Note: The SET clause is optional.
If any of the columns of the table were defined using the optional constraints clause or the optional defaults clause then those are processed on a per row basis. The details are discussed in the "Constraints and defaults" chapter below the CREATE TABLE statement documentation.
System Tables ¶
To allow to query for DB meta data, there exist specially named tables, some of them being virtual.
Note: Virtual system tables may have fake table-wise unique but meaningless and unstable record IDs. Do not apply the built-in id() to any system table.
Tables Table ¶
The table __Table lists all tables in the DB. The schema is
CREATE TABLE __Table (Name string, Schema string);
The Schema column returns the statement to (re)create table Name. This table is virtual.
Columns Table ¶
The table __Colum lists all columns of all tables in the DB. The schema is
CREATE TABLE __Column (TableName string, Ordinal int, Name string, Type string);
The Ordinal column defines the 1-based index of the column in the record. This table is virtual.
Columns2 Table ¶
The table __Colum2 lists all columns of all tables in the DB which have the constraint NOT NULL or which have a constraint expression defined or which have a default expression defined. The schema is
CREATE TABLE __Column2 (TableName string, Name string, NotNull bool, ConstraintExpr string, DefaultExpr string)
It's possible to obtain a consolidated recordset for all properties of all DB columns using
SELECT __Column.TableName, __Column.Ordinal, __Column.Name, __Column.Type, __Column2.NotNull, __Column2.ConstraintExpr, __Column2.DefaultExpr, FROM __Column LEFT JOIN __Column2 ON __Column.TableName == __Column2.TableName && __Column.Name == __Column2.Name ORDER BY __Column.TableName, __Column.Ordinal;
The Name column is the column name in TableName.
Indices table ¶
The table __Index lists all indices in the DB. The schema is
CREATE TABLE __Index (TableName string, ColumnName string, Name string, IsUnique bool);
The IsUnique columns reflects if the index was created using the optional UNIQUE clause. This table is virtual.
Built-in functions ¶
Built-in functions are predeclared.
Average ¶
The built-in aggregate function avg returns the average of values of an expression. Avg ignores NULL values, but returns NULL if all values of a column are NULL or if avg is applied to an empty record set.
func avg(e numeric) typeof(e)
The column values must be of a numeric type.
SELECT salesperson, avg(sales) FROM salesforce GROUP BY salesperson;
Coalesce ¶
The built-in function coalesce takes at least one argument and returns the first of its arguments which is not NULL. If all arguments are NULL, this function returns NULL. This is useful for providing defaults for NULL values in a select query.
func coalesce(args ...interface{}) interface{}
Contains ¶
The built-in function contains returns true if substr is within s.
func contains(s, substr string) bool
If any argument to contains is NULL the result is NULL.
Count ¶
The built-in aggregate function count returns how many times an expression has a non NULL values or the number of rows in a record set. Note: count() returns 0 for an empty record set.
func count() int // The number of rows in a record set. func count(*) int // Equivalent to count(). func count(e expression) int // The number of cases where the expression value is not NULL.
For example
SELECT count() FROM department; // # of rows SELECT count(*) FROM department; // # of rows SELECT count(DepartmentID) FROM department; // # of records with non NULL field DepartmentID SELECT count()-count(DepartmentID) FROM department; // # of records with NULL field DepartmentID SELECT count(foo+bar*3) AS y FROM t; // # of cases where 'foo+bar*3' is non NULL
Date ¶
Date returns the time corresponding to
yyyy-mm-dd hh:mm:ss + nsec nanoseconds
in the appropriate zone for that time in the given location.
The month, day, hour, min, sec, and nsec values may be outside their usual ranges and will be normalized during the conversion. For example, October 32 converts to November 1.
A daylight savings time transition skips or repeats times. For example, in the United States, March 13, 2011 2:15am never occurred, while November 6, 2011 1:15am occurred twice. In such cases, the choice of time zone, and therefore the time, is not well-defined. Date returns a time that is correct in one of the two zones involved in the transition, but it does not guarantee which.
func date(year, month, day, hour, min, sec, nsec int, loc string) time
A location maps time instants to the zone in use at that time. Typically, the location represents the collection of time offsets in use in a geographical area, such as "CEST" and "CET" for central Europe. "local" represents the system's local time zone. "UTC" represents Universal Coordinated Time (UTC).
The month specifies a month of the year (January = 1, ...).
If any argument to date is NULL the result is NULL.
Day ¶
The built-in function day returns the day of the month specified by t.
func day(t time) int
If the argument to day is NULL the result is NULL.
Format time ¶
The built-in function formatTime returns a textual representation of the time value formatted according to layout, which defines the format by showing how the reference time,
Mon Jan 2 15:04:05 -0700 MST 2006
would be displayed if it were the value; it serves as an example of the desired output. The same display rules will then be applied to the time value.
func formatTime(t time, layout string) string
If any argument to formatTime is NULL the result is NULL.
NOTE: The string value of the time zone, like "CET" or "ACDT", is dependent on the time zone of the machine the function is run on. For example, if the t value is in "CET", but the machine is in "ACDT", instead of "CET" the result is "+0100". This is the same what Go (time.Time).String() returns and in fact formatTime directly calls t.String().
formatTime(date(2006, 1, 2, 15, 4, 5, 999999999, "CET"))
returns
2006-01-02 15:04:05.999999999 +0100 CET
on a machine in the CET time zone, but may return
2006-01-02 15:04:05.999999999 +0100 +0100
on a machine in the ACDT zone. The time value is in both cases the same so its ordering and comparing is correct. Only the display value can differ.
Format numbers ¶
The built-in functions formatFloat and formatInt format numbers to strings using go's number format functions in the `strconv` package. For all three functions, only the first argument is mandatory. The default values of the rest are shown in the examples. If the first argument is NULL, the result is NULL.
formatFloat(43.2[, 'g', -1, 64]) string
returns
"43.2" formatInt(-42[, 10]) string
returns
"-42" formatInt(uint32(42)[, 10]) string
returns
"42"
Unlike the `strconv` equivalent, the formatInt function handles all integer types, both signed and unsigned.
HasPrefix ¶
The built-in function hasPrefix tests whether the string s begins with prefix.
func hasPrefix(s, prefix string) bool
If any argument to hasPrefix is NULL the result is NULL.
HasSuffix ¶
The built-in function hasSuffix tests whether the string s ends with suffix.
func hasSuffix(s, suffix string) bool
If any argument to hasSuffix is NULL the result is NULL.
Hour ¶
The built-in function hour returns the hour within the day specified by t, in the range [0, 23].
func hour(t time) int
If the argument to hour is NULL the result is NULL.
Hours ¶
The built-in function hours returns the duration as a floating point number of hours.
func hours(d duration) float
If the argument to hours is NULL the result is NULL.
Record id ¶
The built-in function id takes zero or one arguments. If no argument is provided, id() returns a table-unique automatically assigned numeric identifier of type int. Ids of deleted records are not reused unless the DB becomes completely empty (has no tables).
func id() int
For example
SELECT id(), LastName FROM employee;
If id() without arguments is called for a row which is not a table record then the result value is NULL.
For example
SELECT id(), e.LastName, e.DepartmentID, d.DepartmentID FROM employee AS e, department AS d, WHERE e.DepartmentID == d.DepartmentID; // Will always return NULL in first field. SELECT e.ID, e.LastName, e.DepartmentID, d.DepartmentID FROM (SELECT id() AS ID, LastName, DepartmentID FROM employee) AS e, department as d, WHERE e.DepartmentID == d.DepartmentID; // Will work.
If id() has one argument it must be a table name of a table in a cross join.
For example
SELECT * FROM foo, bar WHERE bar.fooID == id(foo) ORDER BY id(foo);
Length ¶
The built-in function len takes a string argument and returns the lentgh of the string in bytes.
func len(s string) int
The expression len(s) is constant if s is a string constant.
If the argument to len is NULL the result is NULL.
Maximum ¶
The built-in aggregate function max returns the largest value of an expression in a record set. Max ignores NULL values, but returns NULL if all values of a column are NULL or if max is applied to an empty record set.
func max(e expression) typeof(e) // The largest value of the expression.
The expression values must be of an ordered type.
For example
SELECT department, max(sales) FROM t GROUP BY department;
Minimum ¶
The built-in aggregate function min returns the smallest value of an expression in a record set. Min ignores NULL values, but returns NULL if all values of a column are NULL or if min is applied to an empty record set.
func min(e expression) typeof(e) // The smallest value of the expression.
For example
SELECT a, min(b) FROM t GROUP BY a;
The column values must be of an ordered type.
Minute ¶
The built-in function minute returns the minute offset within the hour specified by t, in the range [0, 59].
func minute(t time) int
If the argument to minute is NULL the result is NULL.
Minutes ¶
The built-in function minutes returns the duration as a floating point number of minutes.
func minutes(d duration) float
If the argument to minutes is NULL the result is NULL.
Month ¶
The built-in function month returns the month of the year specified by t (January = 1, ...).
func month(t time) int
If the argument to month is NULL the result is NULL.
Nanosecond ¶
The built-in function nanosecond returns the nanosecond offset within the second specified by t, in the range [0, 999999999].
func nanosecond(t time) int
If the argument to nanosecond is NULL the result is NULL.
Nanoseconds ¶
The built-in function nanoseconds returns the duration as an integer nanosecond count.
func nanoseconds(d duration) float
If the argument to nanoseconds is NULL the result is NULL.
Now ¶
The built-in function now returns the current local time.
func now() time
Parse time ¶
The built-in function parseTime parses a formatted string and returns the time value it represents. The layout defines the format by showing how the reference time,
Mon Jan 2 15:04:05 -0700 MST 2006
would be interpreted if it were the value; it serves as an example of the input format. The same interpretation will then be made to the input string.
Elements omitted from the value are assumed to be zero or, when zero is impossible, one, so parsing "3:04pm" returns the time corresponding to Jan 1, year 0, 15:04:00 UTC (note that because the year is 0, this time is before the zero Time). Years must be in the range 0000..9999. The day of the week is checked for syntax but it is otherwise ignored.
In the absence of a time zone indicator, parseTime returns a time in UTC.
When parsing a time with a zone offset like -0700, if the offset corresponds to a time zone used by the current location, then parseTime uses that location and zone in the returned time. Otherwise it records the time as being in a fabricated location with time fixed at the given zone offset.
When parsing a time with a zone abbreviation like MST, if the zone abbreviation has a defined offset in the current location, then that offset is used. The zone abbreviation "UTC" is recognized as UTC regardless of location. If the zone abbreviation is unknown, Parse records the time as being in a fabricated location with the given zone abbreviation and a zero offset. This choice means that such a time can be parses and reformatted with the same layout losslessly, but the exact instant used in the representation will differ by the actual zone offset. To avoid such problems, prefer time layouts that use a numeric zone offset.
func parseTime(layout, value string) time
If any argument to parseTime is NULL the result is NULL.
Second ¶
The built-in function second returns the second offset within the minute specified by t, in the range [0, 59].
func second(t time) int
If the argument to second is NULL the result is NULL.
Seconds ¶
The built-in function seconds returns the duration as a floating point number of seconds.
func seconds(d duration) float
If the argument to seconds is NULL the result is NULL.
Since ¶
The built-in function since returns the time elapsed since t. It is shorthand for now()-t.
func since(t time) duration
If the argument to since is NULL the result is NULL.
Sum ¶
The built-in aggregate function sum returns the sum of values of an expression for all rows of a record set. Sum ignores NULL values, but returns NULL if all values of a column are NULL or if sum is applied to an empty record set.
func sum(e expression) typeof(e) // The sum of the values of the expression.
The column values must be of a numeric type.
SELECT salesperson, sum(sales) FROM salesforce GROUP BY salesperson;
Time in a specific zone ¶
The built-in function timeIn returns t with the location information set to loc. For discussion of the loc argument please see date().
func timeIn(t time, loc string) time
If any argument to timeIn is NULL the result is NULL.
Weekday ¶
The built-in function weekday returns the day of the week specified by t. Sunday == 0, Monday == 1, ...
func weekday(t time) int
If the argument to weekday is NULL the result is NULL.
Year ¶
The built-in function year returns the year in which t occurs.
func year(t time) int
If the argument to year is NULL the result is NULL.
Year day ¶
The built-in function yearDay returns the day of the year specified by t, in the range [1,365] for non-leap years, and [1,366] in leap years.
func yearDay(t time) int
If the argument to yearDay is NULL the result is NULL.
Manipulating complex numbers ¶
Three functions assemble and disassemble complex numbers. The built-in function complex constructs a complex value from a floating-point real and imaginary part, while real and imag extract the real and imaginary parts of a complex value.
complex(realPart, imaginaryPart floatT) complexT real(complexT) floatT imag(complexT) floatT
The type of the arguments and return value correspond. For complex, the two arguments must be of the same floating-point type and the return type is the complex type with the corresponding floating-point constituents: complex64 for float32, complex128 for float64. The real and imag functions together form the inverse, so for a complex value z, z == complex(real(z), imag(z)).
If the operands of these functions are all constants, the return value is a constant.
complex(2, -2) // complex128 complex(1.0, -1.4) // complex128 float32(math.Cos(math.Pi/2)) // float32 complex(5, float32(-x)) // complex64 imag(b) // float64 real(complex(5, float32(-x))) // float32
If any argument to any of complex, real, imag functions is NULL the result is NULL.
Size guarantees ¶
For the numeric types, the following sizes are guaranteed
type size in bytes byte, uint8, int8 1 uint16, int16 2 uint32, int32, float32 4 uint, uint64, int, int64, float64, complex64 8 complex128 16
License ¶
Portions of this specification page are modifications based on work[2] created and shared by Google[3] and used according to terms described in the Creative Commons 3.0 Attribution License[4].
This specification is licensed under the Creative Commons Attribution 3.0 License, and code is licensed under a BSD license[5].
References ¶
Links from the above documentation
[1]: http://golang.org/ref/spec#Notation [2]: http://golang.org/ref/spec [3]: http://code.google.com/policies.html [4]: http://creativecommons.org/licenses/by/3.0/ [5]: http://golang.org/LICENSE [6]: http://golang.org/pkg/regexp/#Regexp.MatchString [7]: http://developer.mimer.com/validator/sql-reserved-words.tml [8]: http://godoc.org/modernc.org/zappy [9]: http://www.w3schools.com/sql/sql_default.asp [10]: http://en.wikipedia.org/wiki/Join_(SQL)#Outer_join
Implementation details ¶
This section is not part of the specification.
Indices ¶
WARNING: The implementation of indices is new and it surely needs more time to become mature.
Indices are used currently used only by the WHERE clause. The following expression patterns of 'WHERE expression' are recognized and trigger index use.
- WHERE c // For bool typed indexed column c
- WHERE !c // For bool typed indexed column c
- WHERE c relOp constExpr // For indexed column c
- WHERE c relOp parameter // For indexed column c
- WHERE parameter relOp c // For indexed column c
- WHERE constExpr relOp c // For indexed column c
The relOp is one of the relation operators <, <=, ==, >=, >. For the equality operator both operands must be of comparable types. For all other operators both operands must be of ordered types. The constant expression is a compile time constant expression. Some constant folding is still a TODO. Parameter is a QL parameter ($1 etc.).
Query rewriting ¶
Consider tables t and u, both with an indexed field f. The WHERE expression doesn't comply with the above simple detected cases.
SELECT * FROM t, u WHERE t.f < x && u.f < y;
However, such query is now automatically rewritten to
SELECT * FROM (SELECT * FROM t WHERE f < x), (SELECT * FROM u WHERE f < y);
which will use both of the indices. The impact of using the indices can be substantial (cf. BenchmarkCrossJoin*) if the resulting rows have low "selectivity", ie. only few rows from both tables are selected by the respective WHERE filtering.
Note: Existing QL DBs can be used and indices can be added to them. However, once any indices are present in the DB, the old QL versions cannot work with such DB anymore.
Benchmarks ¶
Running a benchmark with -v (-test.v) outputs information about the scale used to report records/s and a brief description of the benchmark. For example
$ go test -run NONE -bench 'SelectMem.*1e[23]' -v PASS BenchmarkSelectMem1kBx1e2 50000 67680 ns/op 1477537.05 MB/s --- BENCH: BenchmarkSelectMem1kBx1e2 all_test.go:310: ============================================================= NOTE: All benchmarks report records/s as 1000000 bytes/s. ============================================================= all_test.go:321: Having a table of 100 records, each of size 1kB, measure the performance of SELECT * FROM t; BenchmarkSelectMem1kBx1e3 5000 634819 ns/op 1575251.01 MB/s --- BENCH: BenchmarkSelectMem1kBx1e3 all_test.go:321: Having a table of 1000 records, each of size 1kB, measure the performance of SELECT * FROM t; ok modernc.org/ql 7.496s $
Running the full suite of benchmarks takes a lot of time. Use the -timeout flag to avoid them being killed after the default time limit (10 minutes).
Example (Id) ¶
db, err := OpenMem()
if err != nil {
panic(err)
}
rss, _, err := db.Run(NewRWCtx(), `
BEGIN TRANSACTION;
CREATE TABLE foo (i int);
INSERT INTO foo VALUES (10), (20);
CREATE TABLE bar (fooID int, s string);
INSERT INTO bar SELECT id(), "ten" FROM foo WHERE i == 10;
INSERT INTO bar SELECT id(), "twenty" FROM foo WHERE i == 20;
COMMIT;
SELECT *
FROM foo, bar
WHERE bar.fooID == id(foo)
ORDER BY id(foo);`,
)
if err != nil {
panic(err)
}
for _, rs := range rss {
if err := rs.Do(false, func(data []interface{}) (bool, error) {
fmt.Println(data)
return true, nil
}); err != nil {
panic(err)
}
fmt.Println("----")
}
Output: [10 1 ten] [20 2 twenty] ----
Example (LIKE) ¶
db, err := OpenMem()
if err != nil {
panic(err)
}
rss, _, err := db.Run(NewRWCtx(), `
BEGIN TRANSACTION;
CREATE TABLE t (i int, s string);
INSERT INTO t VALUES
(1, "seafood"),
(2, "A fool on the hill"),
(3, NULL),
(4, "barbaz"),
(5, "foobar"),
;
COMMIT;
SELECT * FROM t WHERE s LIKE "foo" ORDER BY i;
SELECT * FROM t WHERE s LIKE "^bar" ORDER BY i;
SELECT * FROM t WHERE s LIKE "bar$" ORDER BY i;
SELECT * FROM t WHERE !(s LIKE "foo") ORDER BY i;`,
)
if err != nil {
panic(err)
}
for _, rs := range rss {
if err := rs.Do(false, func(data []interface{}) (bool, error) {
fmt.Println(data)
return true, nil
}); err != nil {
panic(err)
}
fmt.Println("----")
}
Output: [1 seafood] [2 A fool on the hill] [5 foobar] ---- [4 barbaz] ---- [5 foobar] ---- [4 barbaz] ----
Example (RecordsetFields) ¶
// See RecordSet.Fields documentation
db, err := OpenMem()
if err != nil {
panic(err)
}
rs, _, err := db.Run(NewRWCtx(), `
BEGIN TRANSACTION;
CREATE TABLE t (s string, i int);
CREATE TABLE u (s string, i int);
INSERT INTO t VALUES
("a", 1),
("a", 2),
("b", 3),
("b", 4),
;
INSERT INTO u VALUES
("A", 10),
("A", 20),
("B", 30),
("B", 40),
;
COMMIT;
SELECT t.s+u.s as a, t.i+u.i as b, "noName", "name" as Named FROM t, u;
SELECT DISTINCT s as S, sum(i) as I FROM (
SELECT t.s+u.s as s, t.i+u.i, 3 as i FROM t, u;
)
GROUP BY s
ORDER BY I;
SELECT DISTINCT * FROM (
SELECT t.s+u.s as S, t.i+u.i, 3 as I FROM t, u;
)
WHERE I < $1
ORDER BY S;
`, 42)
if err != nil {
panic(err)
}
for i, v := range rs {
fields, err := v.Fields()
switch {
case err != nil:
fmt.Printf("Fields[%d]: error: %s\n", i, err)
default:
fmt.Printf("Fields[%d]: %#v\n", i, fields)
}
}
Output: Fields[0]: []string{"a", "b", "", "Named"} Fields[1]: []string{"S", "I"} Fields[2]: []string{"S", "", "I"}
Index ¶
- Constants
- func IsDuplicateUniqueIndexError(err error) bool
- func Marshal(v interface{}) ([]interface{}, error)
- func MustMarshal(v interface{}) []interface{}
- func RegisterDriver()
- func RegisterDriver2()
- func RegisterMemDriver()
- func Unmarshal(v interface{}, data []interface{}) (err error)
- func WalName(dbname string) (r string)
- type ColumnInfo
- type DB
- func (db *DB) Close() error
- func (db *DB) Execute(ctx *TCtx, l List, arg ...interface{}) (rs []Recordset, index int, err error)
- func (db *DB) Flush() (err error)
- func (db *DB) Info() (r *DbInfo, err error)
- func (db *DB) Name() string
- func (db *DB) NewHTTPFS(query string) (*HTTPFS, error)
- func (db *DB) Run(ctx *TCtx, ql string, arg ...interface{}) (rs []Recordset, index int, err error)
- type DbInfo
- type HTTPFS
- type HTTPFile
- func (f *HTTPFile) Close() error
- func (f *HTTPFile) IsDir() bool
- func (f *HTTPFile) ModTime() time.Time
- func (f *HTTPFile) Mode() os.FileMode
- func (f *HTTPFile) Name() string
- func (f *HTTPFile) Read(b []byte) (int, error)
- func (f *HTTPFile) Readdir(count int) ([]os.FileInfo, error)
- func (f *HTTPFile) Seek(offset int64, whence int) (int64, error)
- func (f *HTTPFile) Size() int64
- func (f *HTTPFile) Stat() (os.FileInfo, error)
- func (f *HTTPFile) Sys() interface{}
- type IndexInfo
- type List
- type Options
- type Recordset
- type SchemaOptions
- type StructField
- type StructIndex
- type StructInfo
- type TCtx
- type TableInfo
- type Type
Examples ¶
Constants ¶
const ( BigInt Type = qBigInt BigRat = qBigRat Blob = qBlob Bool = qBool Complex128 = qComplex128 Complex64 = qComplex64 Duration = qDuration Float32 = qFloat32 Float64 = qFloat64 Int16 = qInt16 Int32 = qInt32 Int64 = qInt64 Int8 = qInt8 String = qString Time = qTime Uint16 = qUint16 Uint32 = qUint32 Uint64 = qUint64 Uint8 = qUint8 )
Values of ColumnInfo.Type.
Variables ¶
This section is empty.
Functions ¶
func IsDuplicateUniqueIndexError ¶ added in v1.2.0
IsDuplicateUniqueIndexError reports whether err is produced by attempting to violate unique index constraints.
func Marshal ¶
func Marshal(v interface{}) ([]interface{}, error)
Marshal converts, in the order of appearance, fields of a struct instance v to []interface{} or an error, if any. Value v can be also a pointer to a struct.
Every considered struct field type must be one of the QL types or a type convertible to string, bool, int*, uint*, float* or complex* type or pointer to such type. Integers with a width dependent on the architecture can not be used. Only exported fields are considered. If an exported field QL tag contains "-" then such field is not considered. A QL tag is a struct tag part prefixed by "ql:". Field with name ID, having type int64, corresponds to id() - and is thus not part of the result.
Marshal is safe for concurrent use by multiple goroutines.
Example ¶
type myInt int16
type myString string
type item struct {
ID int64
Name myString
Qty *myInt // pointer enables nil values
Bar int8
}
schema := MustSchema((*item)(nil), "", nil)
ins := MustCompile(`
BEGIN TRANSACTION;
INSERT INTO item VALUES($1, $2, $3);
COMMIT;`,
)
db, err := OpenMem()
if err != nil {
panic(err)
}
ctx := NewRWCtx()
if _, _, err := db.Execute(ctx, schema); err != nil {
panic(err)
}
if _, _, err := db.Execute(ctx, ins, MustMarshal(&item{Name: "foo", Bar: -1})...); err != nil {
panic(err)
}
q := myInt(42)
if _, _, err := db.Execute(ctx, ins, MustMarshal(&item{Name: "bar", Qty: &q})...); err != nil {
panic(err)
}
rs, _, err := db.Run(nil, "SELECT * FROM item ORDER BY id();")
if err != nil {
panic(err)
}
if err = rs[0].Do(true, func(data []interface{}) (bool, error) {
fmt.Println(data)
return true, nil
}); err != nil {
panic(err)
}
Output: [Name Qty Bar] [foo <nil> -1] [bar 42 0]
func MustMarshal ¶
func MustMarshal(v interface{}) []interface{}
MustMarshal is like Marshal but panics on error. It simplifies marshaling of "safe" types, like eg. those which were already verified by Schema or MustSchema. When the underlying Marshal returns an error, MustMarshal panics.
MustMarshal is safe for concurrent use by multiple goroutines.
func RegisterDriver ¶
func RegisterDriver()
RegisterDriver registers a QL database/sql/driver[0] named "ql". The name parameter of
sql.Open("ql", name)
is interpreted as a path name to a named DB file which will be created if not present. The underlying QL database data are persisted on db.Close(). RegisterDriver can be safely called multiple times, it'll register the driver only once.
The name argument can be optionally prefixed by "file://". In that case the prefix is stripped before interpreting it as a file name.
The name argument can be optionally prefixed by "memory://". In that case the prefix is stripped before interpreting it as a name of a memory-only, volatile DB.
The ql2 driver can open both the original (V1) files and the new (V2) ones. It defaults to V1 on creating a new database.
[0]: http://golang.org/pkg/database/sql/driver/
func RegisterDriver2 ¶
func RegisterDriver2()
RegisterDriver2 registers a QL database/sql/driver[0] named "ql2". The name parameter of
sql.Open("ql2", name)
is interpreted as a path name to a named DB file which will be created if not present. The underlying QL database data are persisted on db.Close(). RegisterDriver can be safely called multiple times, it'll register the driver only once.
The name argument can be optionally prefixed by "file://". In that case the prefix is stripped before interpreting it as a file name.
The name argument can be optionally prefixed by "memory://". In that case the prefix is stripped before interpreting it as a name of a memory-only, volatile DB.
The ql2 driver can open both the original (V1) files and the new (V2) ones. It defaults to V2 on creating a new database.
[0]: http://golang.org/pkg/database/sql/driver/
func RegisterMemDriver ¶
func RegisterMemDriver()
RegisterMemDriver registers a QL memory database/sql/driver[0] named "ql-mem". The name parameter of
sql.Open("ql-mem", name)
is interpreted as an unique memory DB name which will be created if not present. The underlying QL memory database data are not persisted on db.Close(). RegisterMemDriver can be safely called multiple times, it'll register the driver only once.
[0]: http://golang.org/pkg/database/sql/driver/
func Unmarshal ¶
func Unmarshal(v interface{}, data []interface{}) (err error)
Unmarshal stores data from []interface{} in the struct value pointed to by v.
Every considered struct field type must be one of the QL types or a type convertible to string, bool, int*, uint*, float* or complex* type or pointer to such type. Integers with a width dependent on the architecture can not be used. Only exported fields are considered. If an exported field QL tag contains "-" then such field is not considered. A QL tag is a struct tag part prefixed by "ql:". Fields are considered in the order of appearance. Types of values in data must be compatible with the corresponding considered field of v.
If the struct has no ID field then the number of values in data must be equal to the number of considered fields of v.
type T struct {
A bool
B string
}
Assuming the schema is
CREATE TABLE T (A bool, B string);
Data might be a result of queries like
SELECT * FROM T; SELECT A, B FROM T;
If the struct has a considered ID field then the number of values in data must be equal to the number of considered fields in v - or one less. In the later case the ID field is not set.
type U struct {
ID int64
A bool
B string
}
Assuming the schema is
CREATE TABLE T (A bool, B string);
Data might be a result of queries like
SELECT * FROM T; // ID not set SELECT A, B FROM T; // ID not set SELECT id(), A, B FROM T; // ID is set
To unmarshal a value from data into a pointer field of v, Unmarshal first handles the case of the value being nil. In that case, Unmarshal sets the pointer to nil. Otherwise, Unmarshal unmarshals the data value into value pointed at by the pointer. If the pointer is nil, Unmarshal allocates a new value for it to point to.
Unmarshal is safe for concurrent use by multiple goroutines.
Example ¶
type myString string
type row struct {
ID int64
S myString
P *int64
}
schema := MustSchema((*row)(nil), "", nil)
ins := MustCompile(`
BEGIN TRANSACTION;
INSERT INTO row VALUES($1, $2);
COMMIT;`,
)
sel := MustCompile(`
SELECT id(), S, P FROM row ORDER by id();
SELECT * FROM row ORDER by id();`,
)
db, err := OpenMem()
if err != nil {
panic(err)
}
ctx := NewRWCtx()
if _, _, err = db.Execute(ctx, schema); err != nil {
panic(err)
}
r := &row{S: "foo"}
if _, _, err = db.Execute(ctx, ins, MustMarshal(r)...); err != nil {
panic(err)
}
i42 := int64(42)
r = &row{S: "bar", P: &i42}
if _, _, err = db.Execute(ctx, ins, MustMarshal(r)...); err != nil {
panic(err)
}
rs, _, err := db.Execute(nil, sel)
if err != nil {
panic(err)
}
for _, rs := range rs {
fmt.Println("----")
if err := rs.Do(false, func(data []interface{}) (bool, error) {
r := &row{}
if err := Unmarshal(r, data); err != nil {
return false, err
}
fmt.Printf("ID %d, S %q, P ", r.ID, r.S)
switch r.P == nil {
case true:
fmt.Println("<nil>")
default:
fmt.Println(*r.P)
}
return true, nil
}); err != nil {
panic(err)
}
}
Output: ---- ID 1, S "foo", P <nil> ID 2, S "bar", P 42 ---- ID 0, S "foo", P <nil> ID 0, S "bar", P 42
Types ¶
type ColumnInfo ¶
type ColumnInfo struct {
Name string // Column name.
Type Type // Column type (BigInt, BigRat, ...).
NotNull bool // Column cannot be NULL.
Constraint string // Constraint expression, if any.
Default string // Default expression, if any.
}
ColumnInfo provides meta data describing a table column.
type DB ¶
type DB struct {
// contains filtered or unexported fields
}
DB represent the database capable of executing QL statements.
func OpenFile ¶
OpenFile returns a DB backed by a named file. The back end limits the size of a record to about 64 kB.
func OpenMem ¶
OpenMem returns a new, empty DB backed by the process' memory. The back end has no limits on field/record/table/DB size other than memory available to the process.
func (*DB) Execute ¶
Execute executes statements in a list while substituting QL parameters from arg.
The resulting []Recordset corresponds to the SELECT FROM statements in the list.
If err != nil then index is the zero based index of the failed QL statement. Empty statements do not count.
The FSM STT describing the relations between DB states, statements and the ctx parameter.
+-----------+---------------------+------------------+------------------+------------------+ |\ Event | | | | | | \-------\ | BEGIN | | | Other | | State \| TRANSACTION | COMMIT | ROLLBACK | statement | +-----------+---------------------+------------------+------------------+------------------+ | RD | if PC == nil | return error | return error | DB.RLock | | | return error | | | Execute(1) | | CC == nil | | | | DB.RUnlock | | TNL == 0 | DB.Lock | | | | | | CC = PC | | | | | | TNL++ | | | | | | DB.BeginTransaction | | | | | | State = WR | | | | +-----------+---------------------+------------------+------------------+------------------+ | WR | if PC == nil | if PC != CC | if PC != CC | if PC == nil | | | return error | return error | return error | DB.Rlock | | CC != nil | | | | Execute(1) | | TNL != 0 | if PC != CC | DB.Commit | DB.Rollback | RUnlock | | | DB.Lock | TNL-- | TNL-- | else if PC != CC | | | CC = PC | if TNL == 0 | if TNL == 0 | return error | | | | CC = nil | CC = nil | else | | | TNL++ | State = RD | State = RD | Execute(2) | | | DB.BeginTransaction | DB.Unlock | DB.Unlock | | +-----------+---------------------+------------------+------------------+------------------+ CC: Curent transaction context PC: Passed transaction context TNL: Transaction nesting level
Lock, Unlock, RLock, RUnlock semantics above are the same as in sync.RWMutex.
(1): Statement list is executed outside of a transaction. Attempts to update the DB will fail, the execution context is read-only. Other statements with read only context will execute concurrently. If any statement fails, the execution of the statement list is aborted.
Note that the RLock/RUnlock surrounds every single "other" statement when it is executed outside of a transaction. If read consistency is required by a list of more than one statement then an explicit BEGIN TRANSACTION / COMMIT or ROLLBACK wrapper must be provided. Otherwise the state of the DB may change in between executing any two out-of-transaction statements.
(2): Statement list is executed inside an isolated transaction. Execution of statements can update the DB, the execution context is read-write. If any statement fails, the execution of the statement list is aborted and the DB is automatically rolled back to the TNL which was active before the start of execution of the statement list.
Execute is safe for concurrent use by multiple goroutines, but one must consider the blocking issues as discussed above.
ACID ¶
Atomicity: Transactions are atomic. Transactions can be nested. Commit or rollbacks work on the current transaction level. Transactions are made persistent only on the top level commit. Reads made from within an open transaction are dirty reads.
Consistency: Transactions bring the DB from one structurally consistent state to other structurally consistent state.
Isolation: Transactions are isolated. Isolation is implemented by serialization.
Durability: Transactions are durable. A two phase commit protocol and a write ahead log is used. Database is recovered after a crash from the write ahead log automatically on open.
func (*DB) Flush ¶
Flush ends the transaction collecting window, if applicable. IOW, if the DB is dirty, it schedules a 2PC (WAL + DB file) commit on the next outer most DB.Commit or performs it synchronously if there's currently no open transaction.
The collecting window is an implementation detail and future versions of Flush may become a no operation while keeping the operation semantics.
func (*DB) Info ¶
Info provides meta data describing a DB or an error if any. It locks the DB to obtain the result.
func (*DB) NewHTTPFS ¶
NewHTTPFS returns a http.FileSystem backed by a result record set of query. The record set provides two mandatory fields: path and content (the field names are case sensitive). Type of name must be string and type of content must be blob (ie. []byte). Field 'path' value is the "file" pathname, which must be rooted; and field 'content' value is its "data".
type DbInfo ¶
type DbInfo struct {
Name string // DB name.
Tables []TableInfo // Tables in the DB.
Indices []IndexInfo // Indices in the DB.
}
DbInfo provides meta data describing a DB.
type HTTPFS ¶
type HTTPFS struct {
// contains filtered or unexported fields
}
HTTPFS implements a http.FileSystem backed by data in a DB.
type HTTPFile ¶
type HTTPFile struct {
// contains filtered or unexported fields
}
A HTTPFile is returned by the HTTPFS's Open method and can be served by the http.FileServer implementation.
type IndexInfo ¶
type IndexInfo struct {
Name string // Index name
Table string // Table name.
Column string // Column name.
Unique bool // Whether the index is unique.
ExpressionList []string // Index expression list.
}
IndexInfo provides meta data describing a DB index. It corresponds to the statement
CREATE INDEX Name ON Table (Column);
type List ¶
type List struct {
// contains filtered or unexported fields
}
List represents a group of compiled statements.
func Compile ¶
Compile parses the ql statements from src and returns a compiled list for DB.Execute or an error if any.
Compile is safe for concurrent use by multiple goroutines.
func MustCompile ¶
MustCompile is like Compile but panics if the ql statements in src cannot be compiled. It simplifies safe initialization of global variables holding compiled statement lists for DB.Execute.
MustCompile is safe for concurrent use by multiple goroutines.
func MustSchema ¶
func MustSchema(v interface{}, name string, opt *SchemaOptions) List
MustSchema is like Schema but panics on error. It simplifies safe initialization of global variables holding compiled schemas.
MustSchema is safe for concurrent use by multiple goroutines.
func Schema ¶
func Schema(v interface{}, name string, opt *SchemaOptions) (List, error)
Schema returns a CREATE TABLE/INDEX statement(s) for a table derived from a struct or an error, if any. The table is named using the name parameter. If name is an empty string then the type name of the struct is used while non conforming characters are replaced by underscores. Value v can be also a pointer to a struct.
Every considered struct field type must be one of the QL types or a type convertible to string, bool, int*, uint*, float* or complex* type or pointer to such type. Integers with a width dependent on the architecture can not be used. Only exported fields are considered. If an exported field QL tag contains "-" (`ql:"-"`) then such field is not considered. A field with name ID, having type int64, corresponds to id() - and is thus not a part of the CREATE statement. A field QL tag containing "index name" or "uindex name" triggers additionally creating an index or unique index on the respective field. Fields can be renamed using a QL tag "name newName". Fields are considered in the order of appearance. A QL tag is a struct tag part prefixed by "ql:". Tags can be combined, for example:
type T struct {
Foo string `ql:"index xFoo, name Bar"`
}
If opts.NoTransaction == true then the statement(s) are not wrapped in a transaction. If opt.NoIfNotExists == true then the CREATE statement(s) omits the IF NOT EXISTS clause. Passing nil opts is equal to passing &SchemaOptions{}
Schema is safe for concurrent use by multiple goroutines.
Example ¶
type department struct {
a int // unexported -> ignored
ID int64 `ql:"index xID"`
Other string `xml:"-" ql:"-"` // ignored by QL tag
DepartmentName string `ql:"name Name, uindex xName" json:"foo"`
m bool
HQ int32
z string
}
schema := MustSchema((*department)(nil), "", nil)
sel := MustCompile(`
SELECT * FROM __Table WHERE !hasPrefix(Name, "__") ORDER BY Name;
SELECT * FROM __Column WHERE !hasPrefix(TableName, "__") ORDER BY TableName, Ordinal;
SELECT * FROM __Index WHERE !hasPrefix(TableName, "__") ORDER BY Name, ColumnName;`,
)
fmt.Print(schema)
db, err := OpenMem()
if err != nil {
panic(err)
}
if _, _, err = db.Execute(NewRWCtx(), schema); err != nil {
panic(err)
}
rs, _, err := db.Execute(nil, sel)
if err != nil {
panic(err)
}
for _, rs := range rs {
fmt.Println("----")
if err = rs.Do(true, func(data []interface{}) (bool, error) {
fmt.Println(data)
return true, nil
}); err != nil {
panic(err)
}
}
Output: BEGIN TRANSACTION; CREATE TABLE IF NOT EXISTS department (Name string, HQ int32); CREATE INDEX IF NOT EXISTS xID ON department (id()); CREATE UNIQUE INDEX IF NOT EXISTS xName ON department (Name); COMMIT; ---- [Name Schema] [department CREATE TABLE department (Name string, HQ int32);] ---- [TableName Ordinal Name Type] [department 1 Name string] [department 2 HQ int32] ---- [TableName ColumnName Name IsUnique] [department id() xID false] [department Name xName true]
func (List) IsExplainStmt ¶
IsExplainStmt reports whether l is a single EXPLAIN statement or a single EXPLAIN statement enclosed in a transaction.
type Options ¶
type Options struct {
CanCreate bool
OSFile lldb.OSFile
TempFile func(dir, prefix string) (f lldb.OSFile, err error)
Headroom int64
RemoveEmptyWAL bool
FileFormat int
}
Options amend the behavior of OpenFile.
CanCreate ¶
The CanCreate option enables OpenFile to create the DB file if it does not exists.
OSFile ¶
OSFile allows to pass an os.File like back end providing, for example, encrypted storage. If this field is nil then OpenFile uses the file named by the 'name' parameter instead.
TempFile ¶
TempFile provides a temporary file used for evaluating the GROUP BY, ORDER BY, ... clauses. The hook is intended to be used by encrypted DB back ends to avoid leaks of unecrypted data to such temp files by providing temp files which are encrypted as well. Note that *os.File satisfies the lldb.OSFile interface.
If TempFile is nil it defaults to ioutil.TempFile.
Headroom ¶
Headroom selects the minimum size a WAL file will have. The "extra" allocated file space serves as a headroom. Commits that fit into the headroom should not fail due to 'not enough space on the volume' errors. The headroom parameter is first rounded-up to a non negative multiple of the size of the lldb.Allocator atom.
RemoveEmptyWAL ¶
RemoveEmptyWAL controls whether empty WAL files should be deleted on clean exit.
FileVersion ¶
Select DB backend format when creating a new DB file.
Supported values
0, 1 The original file format (version 1) 2 File format version 2
type Recordset ¶
type Recordset interface {
Do(names bool, f func(data []interface{}) (more bool, err error)) error
Fields() (names []string, err error)
FirstRow() (row []interface{}, err error)
Rows(limit, offset int) (rows [][]interface{}, err error)
}
Recordset is a result of a select statement. It can call a user function for every row (record) in the set using the Do method.
Recordsets can be safely reused. Evaluation of the rows is performed lazily. Every invocation of Do will see the current, potentially actualized data.
Do ¶
Do will call f for every row (record) in the Recordset.
If f returns more == false or err != nil then f will not be called for any remaining rows in the set and the err value is returned from Do.
If names == true then f is firstly called with a virtual row consisting of field (column) names of the RecordSet.
Do is executed in a read only context and performs a RLock of the database.
Do is safe for concurrent use by multiple goroutines.
Fields ¶
Fields return a slice of field names of the recordset. The result is computed without actually computing the recordset rows.
FirstRow ¶
FirstRow will return the first row of the RecordSet or an error, if any. If the Recordset has no rows the result is (nil, nil).
Rows ¶
Rows will return rows in Recordset or an error, if any. The semantics of limit and offset are the same as of the LIMIT and OFFSET clauses of the SELECT statement. To get all rows pass limit < 0. If there are no rows to return the result is (nil, nil).
type SchemaOptions ¶
type SchemaOptions struct {
// Don't wrap the CREATE statement(s) in a transaction.
NoTransaction bool
// Don't insert the IF NOT EXISTS clause in the CREATE statement(s).
NoIfNotExists bool
// Do not strip the "pkg." part from type name "pkg.Type", produce
// "pkg_Type" table name instead. Applies only when no name is passed
// to Schema().
KeepPrefix bool
}
SchemaOptions amend the result of Schema.
type StructField ¶
type StructField struct {
Index int // Index is the index of the field for reflect.Value.Field.
IsID bool // Whether the field corresponds to record id().
IsPtr bool // Whether the field is a pointer type.
MarshalType reflect.Type // The reflect.Type a field must be converted to when marshaling or nil when it is assignable directly. (Field->value)
Name string // Field name or value of the name tag (like in `ql:"name foo"`).
ReflectType reflect.Type // The reflect.Type of the field.
Tags map[string]string // QL tags of this field. (`ql:"a, b c, d"` -> {"a": "", "b": "c", "d": ""})
Type Type // QL type of the field.
UnmarshalType reflect.Type // The reflect.Type a value must be converted to when unmarshaling or nil when it is assignable directly. (Field<-value)
ZeroPtr reflect.Value // The reflect.Zero value of the field if it's a pointer type.
}
StructField describes a considered field of a struct type.
type StructIndex ¶
type StructIndex struct {
ColumnName string // Name of the column the index is on.
Name string // Name of the index.
Unique bool // Whether the index is unique.
}
StructIndex describes an index defined by the ql tag index or uindex.
type StructInfo ¶
type StructInfo struct {
Fields []*StructField // Fields describe the considered fields of a struct type.
HasID bool // Whether the struct has a considered field named ID of type int64.
Indices []*StructIndex // Indices describe indices defined by the index or uindex ql tags.
IsPtr bool // Whether the StructInfo was derived from a pointer to a struct.
}
StructInfo describes a struct type. An instance of StructInfo obtained from StructSchema is shared and must not be mutated. That includes the values pointed to by the elements of Fields and Indices.
func MustStructSchema ¶
func MustStructSchema(v interface{}) *StructInfo
MustStructSchema is like StructSchema but panics on error. It simplifies safe initialization of global variables holding StructInfo.
MustStructSchema is safe for concurrent use by multiple goroutines.
func StructSchema ¶
func StructSchema(v interface{}) (*StructInfo, error)
StructSchema returns StructInfo for v which must be a struct instance or a pointer to a struct. The info is computed only once for every type. Subsequent calls to StructSchema for the same type return a cached StructInfo.
Note: The returned StructSchema is shared and must be not mutated, including any other data structures it may point to.
type TCtx ¶
TCtx represents transaction context. It enables to execute multiple statement lists in the same context. The same context guarantees the state of the DB cannot change in between the separated executions.
LastInsertID ¶
LastInsertID is updated by INSERT INTO statements. The value considers performed ROLLBACK statements, if any, even though roll backed IDs are not reused. QL clients should treat the field as read only.
RowsAffected ¶
RowsAffected is updated by INSERT INTO, DELETE FROM and UPDATE statements. The value does not (yet) consider any ROLLBACK statements involved. QL clients should treat the field as read only.
Example (LastInsertID) ¶
ins := MustCompile("BEGIN TRANSACTION; INSERT INTO t VALUES ($1); COMMIT;")
db, err := OpenMem()
if err != nil {
panic(err)
}
ctx := NewRWCtx()
if _, _, err = db.Run(ctx, `
BEGIN TRANSACTION;
CREATE TABLE t (c int);
INSERT INTO t VALUES (1), (2), (3);
COMMIT;
`); err != nil {
panic(err)
}
if _, _, err = db.Execute(ctx, ins, int64(42)); err != nil {
panic(err)
}
id := ctx.LastInsertID
rs, _, err := db.Run(ctx, `SELECT * FROM t WHERE id() == $1`, id)
if err != nil {
panic(err)
}
if err = rs[0].Do(false, func(data []interface{}) (more bool, err error) {
fmt.Println(data)
return true, nil
}); err != nil {
panic(err)
}
Output: [42]
type TableInfo ¶
type TableInfo struct {
// Table name.
Name string
// Table schema. Columns are listed in the order in which they appear
// in the schema.
Columns []ColumnInfo
}
TableInfo provides meta data describing a DB table.
Source Files
¶
Directories
¶
| Path | Synopsis |
|---|---|
|
Package design describes some of the data structures used in QL.
|
Package design describes some of the data structures used in QL. |
|
Package driver registers QL sql/drivers named "ql", "ql2" and a memory driver named "ql-mem".
|
Package driver registers QL sql/drivers named "ql", "ql2" and a memory driver named "ql-mem". |
|
Command ql is a utility to explore a database, prototype a schema or test drive a query, etc.
|
Command ql is a utility to explore a database, prototype a schema or test drive a query, etc. |
|
vendored
|
|
|
github.com/camlistore/go4/lock
Package lock is a file locking library.
|
Package lock is a file locking library. |