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## SQL As Understood By SQLite

### expression

expr ::= | expr binary-op expr | expr [NOT] like-op expr [ESCAPE expr] | unary-op expr | ( expr ) | column-name | table-name . column-name | database-name . table-name . column-name | literal-value | parameter | function-name ( expr-list | * ) | expr ISNULL | expr NOTNULL | expr [NOT] BETWEEN expr AND expr | expr [NOT] IN ( value-list ) | expr [NOT] IN ( select-statement ) | expr [NOT] IN [database-name .] table-name | [EXISTS] ( select-statement ) | CASE [expr] ( WHEN expr THEN expr )+ [ELSE expr] END | CAST ( expr AS type ) | expr COLLATE collation-name
like-op ::= | LIKE | GLOB | REGEXP | MATCH

This section is different from the others. Most other sections of this document talks about a particular SQL command. This section does not talk about a standalone command but about "expressions" which are subcomponents of most other commands.

SQLite understands the following binary operators, in order from highest to lowest precedence:

>     ||
>     *    /    %
>     +    -
>     <<   >>   &    |
>     <    <=   >    >=
>     =    ==   !=   <>   IN
>     AND
>     OR

Supported unary prefix operators are these:

>     -    +    !    ~    NOT

The COLLATE operator can be thought of as a unary postfix operator. The COLLATE operator has the highest precedence. It always binds more tightly than any prefix unary operator or any binary operator.

The unary operator [Operator +] is a no-op. It can be applied to strings, numbers, or blobs and it always gives as its result the value of the operand.

Note that there are two variations of the equals and not equals operators. Equals can be either = or ==. The non-equals operator can be either != or <>. The || operator is "concatenate" - it joins together the two strings of its operands. The operator % outputs the remainder of its left operand modulo its right operand.

The result of any binary operator is a numeric value, except for the || concatenation operator which gives a string result.

A literal value is an integer number or a floating point number. Scientific notation is supported. The "." character is always used as the decimal point even if the locale setting specifies "," for this role - the use of "," for the decimal point would result in syntactic ambiguity. A string constant is formed by enclosing the string in single quotes ('). A single quote within the string can be encoded by putting two single quotes in a row - as in Pascal. C-style escapes using the backslash character are not supported because they are not standard SQL. BLOB literals are string literals containing hexadecimal data and preceded by a single "x" or "X" character. For example:

>     X'53514C697465'

A literal value can also be the token "NULL".

A parameter specifies a placeholder in the expression for a literal value that is filled in at runtime using the sqlite3_bind API. Parameters can take several forms:

?NNN |  | A question mark followed by a number NNN holds a spot for the NNN-th parameter. NNN must be between 1 and 999.
? |  | A question mark that is not followed by a number holds a spot for the next unused parameter.
:AAAA |  | A colon followed by an identifier name holds a spot for a named parameter with the name AAAA. Named parameters are also numbered. The number assigned is the next unused number. To avoid confusion, it is best to avoid mixing named and numbered parameters.
@AAAA |  | An "at" sign works exactly like a colon.
$AAAA |  | A dollar-sign followed by an identifier name also holds a spot for a named parameter with the name AAAA. The identifier name in this case can include one or more occurances of "::" and a suffix enclosed in "(...)" containing any text at all. This syntax is the form of a variable name in the Tcl programming language.

Parameters that are not assigned values using sqlite3_bind are treated as NULL.

The LIKE operator does a pattern matching comparison. The operand to the right contains the pattern, the left hand operand contains the string to match against the pattern. A percent symbol % in the pattern matches any sequence of zero or more characters in the string. An underscore _ in the pattern matches any single character in the string. Any other character matches itself or it's lower/upper case equivalent (i.e. case-insensitive matching). (A bug: SQLite only understands upper/lower case for 7-bit Latin characters. Hence the LIKE operator is case sensitive for 8-bit iso8859 characters or UTF-8 characters. For example, the expression 'a' LIKE 'A' is TRUE but 'æ' LIKE 'Æ' is FALSE.).

If the optional ESCAPE clause is present, then the expression following the ESCAPE keyword must evaluate to a string consisting of a single character. This character may be used in the LIKE pattern to include literal percent or underscore characters. The escape character followed by a percent symbol, underscore or itself matches a literal percent symbol, underscore or escape character in the string, respectively. The infix LIKE operator is implemented by calling the user function like(X,Y).

The LIKE operator is not case sensitive and will match upper case characters on one side against lower case characters on the other. (A bug: SQLite only understands upper/lower case for 7-bit Latin characters. Hence the LIKE operator is case sensitive for 8-bit iso8859 characters or UTF-8 characters. For example, the expression 'a' LIKE 'A' is TRUE but 'æ' LIKE 'Æ' is FALSE.).

The infix LIKE operator is implemented by calling the user function like(X,Y). If an ESCAPE clause is present, it adds a third parameter to the function call. If the functionality of LIKE can be overridden by defining an alternative implementation of the like() SQL function.

The GLOB operator is similar to LIKE but uses the Unix file globbing syntax for its wildcards. Also, GLOB is case sensitive, unlike LIKE. Both GLOB and LIKE may be preceded by the NOT keyword to invert the sense of the test. The infix GLOB operator is implemented by calling the user function glob(X,Y) and can be modified by overriding that function.

The REGEXP operator is a special syntax for the regexp() user function. No regexp() user function is defined by default and so use of the REGEXP operator will normally result in an error message. If a user-defined function named "regexp" is added at run-time, that function will be called in order to implement the REGEXP operator.

The MATCH operator is a special syntax for the match() user function. The default match() function implementation raises and exception and is not really useful for anything. But extensions can override the match() function with more helpful logic.

A column name can be any of the names defined in the CREATE TABLE statement or one of the following special identifiers: "ROWID", "OID", or "_ROWID_". These special identifiers all describe the unique integer key (the "row key") associated with every row of every table. The special identifiers only refer to the row key if the CREATE TABLE statement does not define a real column with the same name. Row keys act like read-only columns. A row key can be used anywhere a regular column can be used, except that you cannot change the value of a row key in an UPDATE or INSERT statement. "SELECT * ..." does not return the row key.

SELECT statements can appear in expressions as either the right-hand operand of the IN operator, as a scalar quantity, or as the operand of an EXISTS operator. As a scalar quantity or the operand of an IN operator, the SELECT should have only a single column in its result. Compound SELECTs (connected with keywords like UNION or EXCEPT) are allowed. With the EXISTS operator, the columns in the result set of the SELECT are ignored and the expression returns TRUE if one or more rows exist and FALSE if the result set is empty. If no terms in the SELECT expression refer to value in the containing query, then the expression is evaluated once prior to any other processing and the result is reused as necessary. If the SELECT expression does contain variables from the outer query, then the SELECT is reevaluated every time it is needed.

When a SELECT is the right operand of the IN operator, the IN operator returns TRUE if the result of the left operand is any of the values generated by the select. The IN operator may be preceded by the NOT keyword to invert the sense of the test.

When a SELECT appears within an expression but is not the right operand of an IN operator, then the first row of the result of the SELECT becomes the value used in the expression. If the SELECT yields more than one result row, all rows after the first are ignored. If the SELECT yields no rows, then the value of the SELECT is NULL.

A CAST expression changes the datatype of the into the type specified by <type>. <type> can be any non-empty type name that is valid for the type in a column definition of a CREATE TABLE statement.

Both simple and aggregate functions are supported. A simple function can be used in any expression. Simple functions return a result immediately based on their inputs. Aggregate functions may only be used in a SELECT statement. Aggregate functions compute their result across all rows of the result set.

Core Functions

The core functions shown below are available by default. Additional functions may be written in C and added to the database engine using the sqlite3_create_function() API.

abs(X) | Return the absolute value of argument X.
coalesce(X,Y,...) | Return a copy of the first non-NULL argument. If all arguments are NULL then NULL is returned. There must be at least 2 arguments.
glob(X,Y) | This function is used to implement the "X GLOB Y" syntax of SQLite. The sqlite3_create_function() interface can be used to override this function and thereby change the operation of the GLOB operator.
ifnull(X,Y) | Return a copy of the first non-NULL argument. If both arguments are NULL then NULL is returned. This behaves the same as coalesce() above.
hex(X) | The argument is interpreted as a BLOB. The result is a hexadecimal rendering of the content of that blob.
last_insert_rowid() | Return the ROWID of the last row insert from this connection to the database. This is the same value that would be returned from the sqlite_last_insert_rowid() API function.
length(X) | Return the string length of X in characters. If SQLite is configured to support UTF-8, then the number of UTF-8 characters is returned, not the number of bytes.
like(X,Y) like(X,Y,Z) | This function is used to implement the "X LIKE Y [ESCAPE Z]" syntax of SQL. If the optional ESCAPE clause is present, then the user-function is invoked with three arguments. Otherwise, it is invoked with two arguments only. The sqlite_create_function() interface can be used to override this function and thereby change the operation of the LIKE operator. When doing this, it may be important to override both the two and three argument versions of the like() function. Otherwise, different code may be called to implement the LIKE operator depending on whether or not an ESCAPE clause was specified.
load_extension(X) load_extension(X,Y) | Load SQLite extensions out of the shared library file named X using the entry point Y. The result is a NULL. If Y is omitted then the default entry point of sqlite3_extension_init is used. This function raises an exception if the extension fails to load or initialize correctly. This function will fail if the extension attempts to modify or delete a SQL function or collating sequence. The extension can add new functions or collating sequences, but cannot modify or delete existing functions or collating sequences because those functions and/or collating sequences might be used elsewhere in the currently running SQL statement. To load an extension that changes or deletes functions or collating sequences, use the sqlite3_load_extension() C-language API.
lower(X) | Return a copy of string X will all characters converted to lower case. The C library tolower() routine is used for the conversion, which means that this function might not work correctly on UTF-8 characters.
ltrim(X) ltrim(X,Y) | Return a string formed by removing any and all characters that appear in Y from the left side of X. If the Y argument is omitted, spaces are removed.
max(X,Y,...) | Return the argument with the maximum value. Arguments may be strings in addition to numbers. The maximum value is determined by the usual sort order. Note that max() is a simple function when it has 2 or more arguments but converts to an aggregate function if given only a single argument.
min(X,Y,...) | Return the argument with the minimum value. Arguments may be strings in addition to numbers. The minimum value is determined by the usual sort order. Note that min() is a simple function when it has 2 or more arguments but converts to an aggregate function if given only a single argument.
nullif(X,Y) | Return the first argument if the arguments are different, otherwise return NULL.
quote(X) | This routine returns a string which is the value of its argument suitable for inclusion into another SQL statement. Strings are surrounded by single-quotes with escapes on interior quotes as needed. BLOBs are encoded as hexadecimal literals. The current implementation of VACUUM uses this function. The function is also useful when writing triggers to implement undo/redo functionality.
random(*) | Return a pseudo-random integer between -9223372036854775808 and +9223372036854775807.
replace(X,Y,Z) | Return a string formed by substituting string Z for every occurrance of string Y in string X. The BINARY collating sequence is used for comparisons.
randomblob(N) | Return a N-byte blob containing pseudo-random bytes. N should be a postive integer.
round(X) round(X,Y) | Round off the number X to Y digits to the right of the decimal point. If the Y argument is omitted, 0 is assumed.
rtrim(X) rtrim(X,Y) | Return a string formed by removing any and all characters that appear in Y from the right side of X. If the Y argument is omitted, spaces are removed.
soundex(X) | Compute the soundex encoding of the string X. The string "?000" is returned if the argument is NULL. This function is omitted from SQLite by default. It is only available the -DSQLITE_SOUNDEX=1 compiler option is used when SQLite is built.
sqlite_version(*) | Return the version string for the SQLite library that is running. Example: "2.8.0"
substr(X,Y,Z) substr(X,Y) | Return a substring of input string X that begins with the Y-th character and which is Z characters long. If Z is omitted then all character through the end of the string are returned. The left-most character of X is number 1. If Y is negative the the first character of the substring is found by counting from the right rather than the left. If X is string then characters indices refer to actual UTF-8 characters. If X is a BLOB then the indices refer to bytes.
trim(X) trim(X,Y) | Return a string formed by removing any and all characters that appear in Y from both ends of X. If the Y argument is omitted, spaces are removed.
typeof(X) | Return the type of the expression X. The only return values are "null", "integer", "real", "text", and "blob". SQLite's type handling is explained in Datatypes in SQLite Version 3.
upper(X) | Return a copy of input string X converted to all upper-case letters. The implementation of this function uses the C library routine toupper() which means it may not work correctly on UTF-8 strings.
zeroblob(N) | Return a BLOB consisting of N bytes of 0x00. SQLite manages these zeroblobs very efficiently. Zeroblobs can be used to reserve space for a BLOB that is later written using incremental BLOB I/O.

Date And Time Functions

Date and time functions are documented in the SQLite Wiki.

Aggregate Functions

The aggregate functions shown below are available by default. Additional aggregate functions written in C may be added using the sqlite3_create_function() API.

In any aggregate function that takes a single argument, that argument can be preceeded by the keyword DISTINCT. In such cases, duplicate elements are filtered before being passed into the aggregate function. For example, the function "count(distinct X)" will return the number of distinct values of column X instead of the total number of non-null values in column X.

avg(X) | Return the average value of all non-NULL X within a group. String and BLOB values that do not look like numbers are interpreted as 0. The result of avg() is always a floating point value even if all inputs are integers.
count(X) count(*) | The first form return a count of the number of times that X is not NULL in a group. The second form (with no argument) returns the total number of rows in the group.
max(X) | Return the maximum value of all values in the group. The usual sort order is used to determine the maximum.
min(X) | Return the minimum non-NULL value of all values in the group. The usual sort order is used to determine the minimum. NULL is only returned if all values in the group are NULL.
sum(X) total(X) | Return the numeric sum of all non-NULL values in the group. If there are no non-NULL input rows then sum() returns NULL but total() returns 0.0. NULL is not normally a helpful result for the sum of no rows but the SQL standard requires it and most other SQL database engines implement sum() that way so SQLite does it in the same way in order to be compatible. The non-standard total() function is provided as a convenient way to work around this design problem in the SQL language. The result of total() is always a floating point value. The result of sum() is an integer value if all non-NULL inputs are integers. If any input to sum() is neither an integer or a NULL then sum() returns a floating point value which might be an approximation to the true sum. Sum() will throw an "integer overflow" exception if all inputs are integers or NULL and an integer overflow occurs at any point during the computation. Total() never throws an exception.

This page last modified 2007/11/21 13:59:26 UTC