SQL As Understood By SQLite
The SQLite library understands most of the standard SQL language. But it
does omit some features while at the same time adding a few features of
its own. This document attempts to describe precisely what parts of the
SQL language SQLite does and does not support. A list of keywords is also
provided.
In all of the syntax diagrams that follow, literal text is shown in bold
blue. Non-terminal symbols are shown in italic red. Operators that are
part of the syntactic markup itself are shown in black roman.
This document is just an overview of the SQL syntax implemented by SQLite.
Many low-level productions are omitted. For detailed information on the
language that SQLite understands, refer to the source code and the grammar
file "parse.y".
SQLite implements the follow syntax:
* ALTER TABLE
* ATTACH DATABASE
* BEGIN TRANSACTION
* comment
* COMMIT TRANSACTION
* COPY
* CREATE INDEX
* CREATE TABLE
* CREATE TRIGGER
* CREATE VIEW
* DELETE
* DETACH DATABASE
* DROP INDEX
* DROP TABLE
* DROP TRIGGER
* DROP VIEW
* END TRANSACTION
* EXPLAIN
* expression
* INSERT
* ON CONFLICT clause
* PRAGMA
* REINDEX
* REPLACE
* ROLLBACK TRANSACTION
* SELECT
* UPDATE
* VACUUM
Details on the implementation of each command are provided in the sequel.
--------------------------------------------------------------------------
ALTER TABLE
sql-statement ::= ALTER TABLE [database-name .] table-name
alteration
alteration ::= RENAME TO new-table-name
alteration ::= ADD [COLUMN] column-def
SQLite's version of the ALTER TABLE command allows the user to rename or
add a new column to an existing table. It is not possible to remove a
column from a table.
The RENAME TO syntax is used to rename the table identified by
[database-name.]table-name to new-table-name. This command cannot be used
to move a table between attached databases, only to rename a table within
the same database.
If the table being renamed has triggers or indices, then these remain
attached to the table after it has been renamed. However, if there are any
view definitions, or statements executed by triggers that refer to the
table being renamed, these are not automatically modified to use the new
table name. If this is required, the triggers or view definitions must be
dropped and recreated to use the new table name by hand.
The ADD [COLUMN] syntax is used to add a new column to an existing table.
The new column is always appended to the end of the list of existing
columns. Column-def may take any of the forms permissable in a CREATE
TABLE statement, with the following restrictions:
* The column may not have a PRIMARY KEY or UNIQUE constraint.
* The column may not have a default value of CURRENT_TIME, CURRENT_DATE or
CURRENT_TIMESTAMP.
* If a NOT NULL constraint is specified, then the column must have a
default value other than NULL.
The execution time of the ALTER TABLE command is independent of the
amount of data in the table. The ALTER TABLE command runs as quickly on
a table with 10 million rows as it does on a table with 1 row.
After ADD COLUMN has been run on a database, that database will not be
readable by SQLite version 3.1.3 and earlier until the database is
VACUUMed.
--------------------------------------------------------------------------
ATTACH DATABASE
sql-statement ::= ATTACH [DATABASE] database-filename AS
database-name
The ATTACH DATABASE statement adds a preexisting database file to the
current database connection. If the filename contains punctuation
characters it must be quoted. The names 'main' and 'temp' refer to the
main database and the database used for temporary tables. These cannot
be detached. Attached databases are removed using the DETACH DATABASE
statement.
You can read from and write to an attached database and you can modify
the schema of the attached database. This is a new feature of SQLite
version 3.0. In SQLite 2.8, schema changes to attached databases were
not allowed.
You cannot create a new table with the same name as a table in an
attached database, but you can attach a database which contains tables
whose names are duplicates of tables in the main database. It is also
permissible to attach the same database file multiple times.
Tables in an attached database can be referred to using the syntax
database-name.table-name. If an attached table doesn't have a duplicate
table name in the main database, it doesn't require a database name
prefix. When a database is attached, all of its tables which don't have
duplicate names become the 'default' table of that name. Any tables of
that name attached afterwards require the table prefix. If the 'default'
table of a given name is detached, then the last table of that name
attached becomes the new default.
Transactions involving multiple attached databases are atomic, assuming
that the main database is not ":memory:". If the main database is
":memory:" then transactions continue to be atomic within each
individual database file. But if the host computer crashes in the middle
of a COMMIT where two or more database files are updated, some of those
files might get the changes where others might not. Atomic commit of
attached databases is a new feature of SQLite version 3.0. In SQLite
version 2.8, all commits to attached databases behaved as if the main
database were ":memory:".
There is a compile-time limit of 10 attached database files.
--------------------------------------------------------------------------
BEGIN TRANSACTION
sql-statement ::= BEGIN [ DEFERRED | IMMEDIATE | EXCLUSIVE ]
[TRANSACTION [name]]
sql-statement ::= END [TRANSACTION [name]]
sql-statement ::= COMMIT [TRANSACTION [name]]
sql-statement ::= ROLLBACK [TRANSACTION [name]]
Beginning in version 2.0, SQLite supports transactions with rollback and
atomic commit.
The optional transaction name is ignored. SQLite currently does not
allow nested transactions.
No changes can be made to the database except within a transaction. Any
command that changes the database (basically, any SQL command other than
SELECT) will automatically start a transaction if one is not already in
effect. Automatically started transactions are committed at the
conclusion of the command.
Transactions can be started manually using the BEGIN command. Such
transactions usually persist until the next COMMIT or ROLLBACK command.
But a transaction will also ROLLBACK if the database is closed or if an
error occurs and the ROLLBACK conflict resolution algorithm is
specified. See the documentation on the ON CONFLICT clause for
additional information about the ROLLBACK conflict resolution algorithm.
In SQLite version 3.0.8 and later, transactions can be deferred,
immediate, or exclusive. Deferred means that no locks are acquired on
the database until the database is first accessed. Thus with a deferred
transaction, the BEGIN statement itself does nothing. Locks are not
acquired until the first read or write operation. The first read
operation against a database creates a SHARED lock and the first write
operation creates a RESERVED lock. Because the acquisition of locks is
deferred until they are needed, it is possible that another thread or
process could create a separate transaction and write to the database
after the BEGIN on the current thread has executed. If the transaction
is immediate, then RESERVED locks are acquired on all databases as soon
as the BEGIN command is executed, without waiting for the database to be
used. After a BEGIN IMMEDIATE, you are guaranteed that no other thread
or process will be able to write to the database or do a BEGIN IMMEDIATE
or BEGIN EXCLUSIVE. Other processes can continue to read from the
database, however. An exclusive transaction causes EXCLUSIVE locks to be
acquired on all databases. After a BEGIN EXCLUSIVE, you are guaranteed
that no other thread or process will be able to read or write the
database until the transaction is complete.
A description of the meaning of SHARED, RESERVED, and EXCLUSIVE locks is
available separately.
The default behavior for SQLite version 3.0.8 is a deferred transaction.
For SQLite version 3.0.0 through 3.0.7, deferred is the only kind of
transaction available. For SQLite version 2.8 and earlier, all
transactions are exclusive.
The COMMIT command does not actually perform a commit until all pending
SQL commands finish. Thus if two or more SELECT statements are in the
middle of processing and a COMMIT is executed, the commit will not
actually occur until all SELECT statements finish.
An attempt to execute COMMIT might result in an SQLITE_BUSY return code.
This indicates that another thread or process had a read lock on the
database that prevented the database from being updated. When COMMIT
fails in this way, the transaction remains active and the COMMIT can be
retried later after the reader has had a chance to clear.
--------------------------------------------------------------------------
comment
comment ::= SQL-comment |
C-comment
SQL-comment ::= -- single-line
C-comment ::= /* multiple-lines [*/]
Comments aren't SQL commands, but can occur in SQL queries. They are
treated as whitespace by the parser. They can begin anywhere whitespace
can be found, including inside expressions that span multiple lines.
SQL comments only extend to the end of the current line.
C comments can span any number of lines. If there is no terminating
delimiter, they extend to the end of the input. This is not treated as
an error. A new SQL statement can begin on a line after a multiline
comment ends. C comments can be embedded anywhere whitespace can occur,
including inside expressions, and in the middle of other SQL statements.
C comments do not nest. SQL comments inside a C comment will be ignored.
--------------------------------------------------------------------------
COPY
sql-statement ::= COPY [ OR conflict-algorithm ] [database-name .]
table-name FROM filename
[ USING DELIMITERS delim ]
The COPY command is available in SQLite version 2.8 and earlier. The
COPY command has been removed from SQLite version 3.0 due to
complications in trying to support it in a mixed UTF-8/16 environment.
In version 3.0, the command-line shell contains a new command .import
that can be used as a substitute for COPY.
The COPY command is an extension used to load large amounts of data into
a table. It is modeled after a similar command found in PostgreSQL. In
fact, the SQLite COPY command is specifically designed to be able to
read the output of the PostgreSQL dump utility pg_dump so that data can
be easily transferred from PostgreSQL into SQLite.
The table-name is the name of an existing table which is to be filled
with data. The filename is a string or identifier that names a file from
which data will be read. The filename can be the STDIN to read data from
standard input.
Each line of the input file is converted into a single record in the
table. Columns are separated by tabs. If a tab occurs as data within a
column, then that tab is preceded by a baskslash "\" character. A
baskslash in the data appears as two backslashes in a row. The optional
USING DELIMITERS clause can specify a delimiter other than tab.
If a column consists of the character "\N", that column is filled with
the value NULL.
The optional conflict-clause allows the specification of an alternative
constraint conflict resolution algorithm to use for this one command.
See the section titled ON CONFLICT for additional information.
When the input data source is STDIN, the input can be terminated by a
line that contains only a baskslash and a dot: "\.".
--------------------------------------------------------------------------
CREATE INDEX
sql-statement ::= CREATE [UNIQUE] INDEX [database-name .]
index-name
ON table-name ( column-name [, column-name]* )
[ ON CONFLICT conflict-algorithm ]
column-name ::= name [ COLLATE collation-name] [ ASC | DESC ]
The CREATE INDEX command consists of the keywords "CREATE INDEX"
followed by the name of the new index, the keyword "ON", the name of a
previously created table that is to be indexed, and a parenthesized list
of names of columns in the table that are used for the index key. Each
column name can be followed by one of the "ASC" or "DESC" keywords to
indicate sort order, but the sort order is ignored in the current
implementation. Sorting is always done in ascending order.
The COLLATE clause following each column name defines a collating
sequence used for text entires in that column. The default collating
sequence is the collating sequence defined for that column in the CREATE
TABLE statement. Or if no collating sequence is otherwise defined, the
built-in BINARY collating sequence is used.
There are no arbitrary limits on the number of indices that can be
attached to a single table, nor on the number of columns in an index.
If the UNIQUE keyword appears between CREATE and INDEX then duplicate
index entries are not allowed. Any attempt to insert a duplicate entry
will result in an error.
The optional conflict-clause allows the specification of an alternative
default constraint conflict resolution algorithm for this index. This
only makes sense if the UNIQUE keyword is used since otherwise there are
not constraints on the index. The default algorithm is ABORT. If a COPY,
INSERT, or UPDATE statement specifies a particular conflict resolution
algorithm, that algorithm is used in place of the default algorithm
specified here. See the section titled ON CONFLICT for additional
information.
The exact text of each CREATE INDEX statement is stored in the
sqlite_master or sqlite_temp_master table, depending on whether the
table being indexed is temporary. Every time the database is opened, all
CREATE INDEX statements are read from the sqlite_master table and used
to regenerate SQLite's internal representation of the index layout.
Indexes are removed with the DROP INDEX command.
--------------------------------------------------------------------------
CREATE TABLE
sql-command ::= CREATE [TEMP | TEMPORARY] TABLE table-name (
column-def [, column-def]*
[, constraint]*
)
sql-command ::= CREATE [TEMP | TEMPORARY] TABLE
[database-name.] table-name AS
select-statement
column-def ::= name [type] [[CONSTRAINT name]
column-constraint]*
type ::= typename |
typename ( number ) |
typename ( number , number )
column-constraint ::= NOT NULL [ conflict-clause ] |
PRIMARY KEY [sort-order] [ conflict-clause ]
[AUTOINCREMENT] |
UNIQUE [ conflict-clause ] |
CHECK ( expr ) [ conflict-clause ] |
DEFAULT value |
COLLATE collation-name
constraint ::= PRIMARY KEY ( column-list ) [ conflict-clause
] |
UNIQUE ( column-list ) [ conflict-clause ] |
CHECK ( expr ) [ conflict-clause ]
conflict-clause ::= ON CONFLICT conflict-algorithm
A CREATE TABLE statement is basically the keywords "CREATE TABLE"
followed by the name of a new table and a parenthesized list of column
definitions and constraints. The table name can be either an identifier
or a string. Tables names that begin with "sqlite_" are reserved for use
by the engine.
Each column definition is the name of the column followed by the
datatype for that column, then one or more optional column constraints.
The datatype for the column does not restrict what data may be put in
that column. See Datatypes In SQLite Version 3 for additional
information. The UNIQUE constraint causes an index to be created on the
specified columns. This index must contain unique keys. The COLLATE
clause specifies what text collating function to use when comparing text
entries for the column. The built-in BINARY collating function is used
by default.
The DEFAULT constraint specifies a default value to use when doing an
INSERT. The value may be NULL, a string constant or a number. Starting
with version 3.1.0, the default value may also be one of the special
case-independant keywords CURRENT_TIME, CURRENT_DATE or
CURRENT_TIMESTAMP. If the value is NULL, a string constant or number, it
is literally inserted into the column whenever an INSERT statement that
does not specify a value for the column is executed. If the value is
CURRENT_TIME, CURRENT_DATE or CURRENT_TIMESTAMP, then the current UTC
date and/or time is inserted into the columns. For CURRENT_TIME, the
format is HH:MM:SS. For CURRENT_DATE, YYYY-MM-DD. The format for
CURRENT_TIMESTAMP is "YYYY-MM-DD HH:MM:SS".
Specifying a PRIMARY KEY normally just creates a UNIQUE index on the
corresponding columns. However, if primary key is on a single column
that has datatype INTEGER, then that column is used internally as the
actual key of the B-Tree for the table. This means that the column may
only hold unique integer values. (Except for this one case, SQLite
ignores the datatype specification of columns and allows any kind of
data to be put in a column regardless of its declared datatype.) If a
table does not have an INTEGER PRIMARY KEY column, then the B-Tree key
will be a automatically generated integer. The B-Tree key for a row can
always be accessed using one of the special names "ROWID", "OID", or
"_ROWID_". This is true regardless of whether or not there is an INTEGER
PRIMARY KEY. An INTEGER PRIMARY KEY column man also include the keyword
AUTOINCREMENT. The AUTOINCREMENT keyword modified the way that B-Tree
keys are automatically generated. Additional detail on automatic B-Tree
key generation is available separately.
If the "TEMP" or "TEMPORARY" keyword occurs in between "CREATE" and
"TABLE" then the table that is created is only visible to the process
that opened the database and is automatically deleted when the database
is closed. Any indices created on a temporary table are also temporary.
Temporary tables and indices are stored in a separate file distinct from
the main database file.
If a <database-name> is specified, then the table is created in the
named database. It is an error to specify both a <database-name> and the
TEMP keyword, unless the <database-name> is "temp". If no database name
is specified, and the TEMP keyword is not present, the table is created
in the main database.
The optional conflict-clause following each constraint allows the
specification of an alternative default constraint conflict resolution
algorithm for that constraint. The default is abort ABORT. Different
constraints within the same table may have different default conflict
resolution algorithms. If an COPY, INSERT, or UPDATE command specifies a
different conflict resolution algorithm, then that algorithm is used in
place of the default algorithm specified in the CREATE TABLE statement.
See the section titled ON CONFLICT for additional information.
CHECK constraints are ignored in the current implementation. Support for
CHECK constraints may be added in the future. As of version 2.3.0, NOT
NULL, PRIMARY KEY, and UNIQUE constraints all work.
There are no arbitrary limits on the number of columns or on the number
of constraints in a table. The total amount of data in a single row is
limited to about 1 megabytes in version 2.8. In version 3.0 there is no
arbitrary limit on the amount of data in a row.
The CREATE TABLE AS form defines the table to be the result set of a
query. The names of the table columns are the names of the columns in
the result.
The exact text of each CREATE TABLE statement is stored in the
sqlite_master table. Every time the database is opened, all CREATE TABLE
statements are read from the sqlite_master table and used to regenerate
SQLite's internal representation of the table layout. If the original
command was a CREATE TABLE AS then then an equivalent CREATE TABLE
statement is synthesized and store in sqlite_master in place of the
original command. The text of CREATE TEMPORARY TABLE statements are
stored in the sqlite_temp_master table.
Tables are removed using the DROP TABLE statement.
--------------------------------------------------------------------------
CREATE TRIGGER
sql-statement ::= CREATE [TEMP | TEMPORARY] TRIGGER trigger-name [
BEFORE | AFTER ]
database-event ON [database-name .] table-name
trigger-action
sql-statement ::= CREATE [TEMP | TEMPORARY] TRIGGER trigger-name
INSTEAD OF
database-event ON [database-name .] view-name
trigger-action
database-event ::= DELETE |
INSERT |
UPDATE |
UPDATE OF column-list
trigger-action ::= [ FOR EACH ROW | FOR EACH STATEMENT ] [ WHEN
expression ]
BEGIN
trigger-step ; [ trigger-step ; ]*
END
trigger-step ::= update-statement | insert-statement
|
delete-statement | select-statement
The CREATE TRIGGER statement is used to add triggers to the database
schema. Triggers are database operations (the trigger-action) that are
automatically performed when a specified database event (the
database-event) occurs.
A trigger may be specified to fire whenever a DELETE, INSERT or UPDATE
of a particular database table occurs, or whenever an UPDATE of one or
more specified columns of a table are updated.
At this time SQLite supports only FOR EACH ROW triggers, not FOR EACH
STATEMENT triggers. Hence explicitly specifying FOR EACH ROW is
optional. FOR EACH ROW implies that the SQL statements specified as
trigger-steps may be executed (depending on the WHEN clause) for each
database row being inserted, updated or deleted by the statement causing
the trigger to fire.
Both the WHEN clause and the trigger-steps may access elements of the
row being inserted, deleted or updated using references of the form
"NEW.column-name" and "OLD.column-name", where column-name is the name
of a column from the table that the trigger is associated with. OLD and
NEW references may only be used in triggers on trigger-events for which
they are relevant, as follows:
INSERT NEW references are valid
UPDATE NEW and OLD references are valid
DELETE OLD references are valid
If a WHEN clause is supplied, the SQL statements specified as
trigger-steps are only executed for rows for which the WHEN clause is
true. If no WHEN clause is supplied, the SQL statements are executed for
all rows.
The specified trigger-time determines when the trigger-steps will be
executed relative to the insertion, modification or removal of the
associated row.
An ON CONFLICT clause may be specified as part of an UPDATE or INSERT
trigger-step. However if an ON CONFLICT clause is specified as part of the
statement causing the trigger to fire, then this conflict handling policy
is used instead.
Triggers are automatically dropped when the table that they are associated
with is dropped.
Triggers may be created on views, as well as ordinary tables, by
specifying INSTEAD OF in the CREATE TRIGGER statement. If one or more ON
INSERT, ON DELETE or ON UPDATE triggers are defined on a view, then it is
not an error to execute an INSERT, DELETE or UPDATE statement on the view,
respectively. Thereafter, executing an INSERT, DELETE or UPDATE on the
view causes the associated triggers to fire. The real tables underlying
the view are not modified (except possibly explicitly, by a trigger
program).
Example:
Assuming that customer records are stored in the "customers" table, and
that order records are stored in the "orders" table, the following trigger
ensures that all associated orders are redirected when a customer changes
his or her address:
CREATE TRIGGER update_customer_address UPDATE OF address ON customers
BEGIN
UPDATE orders SET address = new.address WHERE customer_name = old.name;
END;
With this trigger installed, executing the statement:
UPDATE customers SET address = '1 Main St.' WHERE name = 'Jack Jones';
causes the following to be automatically executed:
UPDATE orders SET address = '1 Main St.' WHERE customer_name = 'Jack Jones';
Note that currently, triggers may behave oddly when created on tables with
INTEGER PRIMARY KEY fields. If a BEFORE trigger program modifies the
INTEGER PRIMARY KEY field of a row that will be subsequently updated by
the statement that causes the trigger to fire, then the update may not
occur. The workaround is to declare the table with a PRIMARY KEY column
instead of an INTEGER PRIMARY KEY column.
A special SQL function RAISE() may be used within a trigger-program, with
the following syntax
raise-function ::= RAISE ( ABORT, error-message ) |
RAISE ( FAIL, error-message ) |
RAISE ( ROLLBACK, error-message ) |
RAISE ( IGNORE )
When one of the first three forms is called during trigger-program
execution, the specified ON CONFLICT processing is performed (either
ABORT, FAIL or ROLLBACK) and the current query terminates. An error code
of SQLITE_CONSTRAINT is returned to the user, along with the specified
error message.
When RAISE(IGNORE) is called, the remainder of the current trigger
program, the statement that caused the trigger program to execute and any
subsequent trigger programs that would of been executed are abandoned. No
database changes are rolled back. If the statement that caused the trigger
program to execute is itself part of a trigger program, then that trigger
program resumes execution at the beginning of the next step.
Triggers are removed using the DROP TRIGGER statement. Non-temporary
triggers cannot be added on a table in an attached database.
--------------------------------------------------------------------------
CREATE VIEW
sql-command ::= CREATE [TEMP | TEMPORARY] VIEW [database-name.]
view-name AS select-statement
The CREATE VIEW command assigns a name to a pre-packaged SELECT statement.
Once the view is created, it can be used in the FROM clause of another
SELECT in place of a table name.
If the "TEMP" or "TEMPORARY" keyword occurs in between "CREATE" and
"TABLE" then the table that is created is only visible to the process that
opened the database and is automatically deleted when the database is
closed.
If a <database-name> is specified, then the view is created in the named
database. It is an error to specify both a <database-name> and the TEMP
keyword, unless the <database-name> is "temp". If no database name is
specified, and the TEMP keyword is not present, the table is created in
the main database.
You cannot COPY, DELETE, INSERT or UPDATE a view. Views are read-only in
SQLite. However, in many cases you can use a TRIGGER on the view to
accomplish the same thing. Views are removed with the DROP VIEW command.
Non-temporary views cannot be created on tables in an attached database.
--------------------------------------------------------------------------
DELETE
sql-statement ::= DELETE FROM [database-name .] table-name [WHERE
expr]
The DELETE command is used to remove records from a table. The command
consists of the "DELETE FROM" keywords followed by the name of the table
from which records are to be removed.
Without a WHERE clause, all rows of the table are removed. If a WHERE
clause is supplied, then only those rows that match the expression are
removed.
--------------------------------------------------------------------------
DETACH DATABASE
sql-command ::= DETACH [DATABASE]
database-name
This statement detaches an additional database connection previously
attached using the ATTACH DATABASE statement. It is possible to have the
same database file attached multiple times using different names, and
detaching one connection to a file will leave the others intact.
This statement will fail if SQLite is in the middle of a transaction.
--------------------------------------------------------------------------
DROP INDEX
sql-command ::= DROP INDEX [database-name .]
index-name
The DROP INDEX statement removes an index added with the CREATE INDEX
statement. The index named is completely removed from the disk. The only
way to recover the index is to reenter the appropriate CREATE INDEX
command.
The DROP INDEX statement does not reduce the size of the database file.
Empty space in the database is retained for later INSERTs. To remove free
space in the database, use the VACUUM command.
--------------------------------------------------------------------------
DROP TABLE
sql-command ::= DROP TABLE [database-name.]
table-name
The DROP TABLE statement removes a table added with the CREATE TABLE
statement. The name specified is the table name. It is completely removed
from the database schema and the disk file. The table can not be
recovered. All indices associated with the table are also deleted.
Non-temporary tables in an attached database cannot be dropped.
The DROP TABLE statement does not reduce the size of the database file.
Empty space in the database is retained for later INSERTs. To remove free
space in the database, use the VACUUM command.
--------------------------------------------------------------------------
DROP TRIGGER
sql-statement ::= DROP TRIGGER [database-name .]
trigger-name
The DROP TRIGGER statement removes a trigger created by the CREATE TRIGGER
statement. The trigger is deleted from the database schema. Note that
triggers are automatically dropped when the associated table is dropped.
Non-temporary triggers cannot be dropped on attached tables.
--------------------------------------------------------------------------
DROP VIEW
sql-command ::= DROP VIEW view-name
The DROP VIEW statement removes a view created by the CREATE VIEW
statement. The name specified is the view name. It is removed from the
database schema, but no actual data in the underlying base tables is
modified. Non-temporary views in attached databases cannot be dropped.
--------------------------------------------------------------------------
EXPLAIN
sql-statement ::= EXPLAIN sql-statement
The EXPLAIN command modifier is a non-standard extension. The idea comes
from a similar command found in PostgreSQL, but the operation is
completely different.
If the EXPLAIN keyword appears before any other SQLite SQL command then
instead of actually executing the command, the SQLite library will report
back the sequence of virtual machine instructions it would have used to
execute the command had the EXPLAIN keyword not been present. For
additional information about virtual machine instructions see the
architecture description or the documentation on available opcodes for the
virtual machine.
--------------------------------------------------------------------------
expression
expr ::= expr binary-op expr |
expr like-op expr [ESCAPE expr] |
expr glob-op expr |
unary-op expr |
( expr ) |
column-name |
table-name . column-name |
database-name . table-name . column-name |
literal-value |
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
like-op ::= LIKE | NOT LIKE
glob-op ::= GLOB | NOT GLOB
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 operators are these:
- + ! ~
Any SQLite value can be used as part of an expression. For arithmetic
operations, integers are treated as integers. Strings are first converted
to real numbers using atof(). For comparison operators, numbers compare as
numbers and strings compare using the strcmp() function. 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 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 identical the user
function like(X,Y).
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 identical the user function
glob(X,Y).
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 random
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.
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.
The 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.
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 [,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.
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.
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 random integer between -2147483648 and
+2147483647.
round(X) Round off the number X to Y digits to the right of
round(X,Y) the decimal point. If the Y argument is omitted, 0
is assumed.
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) Return a substring of input string X that begins
with the Y-th character and which is Z characters
long. 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 SQLite is configured to
support UTF-8, then characters indices refer to
actual UTF-8 characters, not bytes.
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.
The following aggregate functions are available by default. Additional
aggregate functions written in C may be added using the
sqlite3_create_function() API.
avg(X) Return the average value of all X within a group.
count(X) The first form return a count of the number of times that X is
count(*) 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) Return the numeric sum of all values in the group.
--------------------------------------------------------------------------
INSERT
sql-statement ::= INSERT [OR conflict-algorithm] INTO [database-name .]
table-name [(column-list)] VALUES(value-list) |
INSERT [OR conflict-algorithm] INTO [database-name .]
table-name [(column-list)] select-statement
The INSERT statement comes in two basic forms. The first form (with the
"VALUES" keyword) creates a single new row in an existing table. If no
column-list is specified then the number of values must be the same as the
number of columns in the table. If a column-list is specified, then the
number of values must match the number of specified columns. Columns of
the table that do not appear in the column list are filled with the
default value, or with NULL if not default value is specified.
The second form of the INSERT statement takes it data from a SELECT
statement. The number of columns in the result of the SELECT must exactly
match the number of columns in the table if no column list is specified,
or it must match the number of columns name in the column list. A new
entry is made in the table for every row of the SELECT result. The SELECT
may be simple or compound. If the SELECT statement has an ORDER BY clause,
the ORDER BY is ignored.
The optional conflict-clause allows the specification of an alternative
constraint conflict resolution algorithm to use during this one command.
See the section titled ON CONFLICT for additional information. For
compatibility with MySQL, the parser allows the use of the single keyword
REPLACE as an alias for "INSERT OR REPLACE".
--------------------------------------------------------------------------
ON CONFLICT clause
conflict-clause ::= ON CONFLICT conflict-algorithm
conflict-algorithm ::= ROLLBACK | ABORT | FAIL | IGNORE | REPLACE
The ON CONFLICT clause is not a separate SQL command. It is a non-standard
clause that can appear in many other SQL commands. It is given its own
section in this document because it is not part of standard SQL and
therefore might not be familiar.
The syntax for the ON CONFLICT clause is as shown above for the CREATE
TABLE and CREATE INDEX commands. For the COPY, INSERT, and UPDATE
commands, the keywords "ON CONFLICT" are replaced by "OR", to make the
syntax seem more natural. But the meaning of the clause is the same either
way.
The ON CONFLICT clause specifies an algorithm used to resolve constraint
conflicts. There are five choices: ROLLBACK, ABORT, FAIL, IGNORE, and
REPLACE. The default algorithm is ABORT. This is what they mean:
ROLLBACK
When a constraint violation occurs, an immediate ROLLBACK occurs,
thus ending the current transaction, and the command aborts with a
return code of SQLITE_CONSTRAINT. If no transaction is active
(other than the implied transaction that is created on every
command) then this algorithm works the same as ABORT.
ABORT
When a constraint violation occurs, the command backs out any
prior changes it might have made and aborts with a return code of
SQLITE_CONSTRAINT. But no ROLLBACK is executed so changes from
prior commands within the same transaction are preserved. This is
the default behavior.
FAIL
When a constraint violation occurs, the command aborts with a
return code SQLITE_CONSTRAINT. But any changes to the database
that the command made prior to encountering the constraint
violation are preserved and are not backed out. For example, if an
UPDATE statement encountered a constraint violation on the 100th
row that it attempts to update, then the first 99 row changes are
preserved but changes to rows 100 and beyond never occur.
IGNORE
When a constraint violation occurs, the one row that contains the
constraint violation is not inserted or changed. But the command
continues executing normally. Other rows before and after the row
that contained the constraint violation continue to be inserted or
updated normally. No error is returned.
REPLACE
When a UNIQUE constraint violation occurs, the pre-existing rows
that are causing the constraint violation are removed prior to
inserting or updating the current row. Thus the insert or update
always occurs. The command continues executing normally. No error
is returned. If a NOT NULL constraint violation occurs, the NULL
value is replaced by the default value for that column. If the
column has no default value, then the ABORT algorithm is used.
When this conflict resolution strategy deletes rows in order to
satisfy a constraint, it does not invoke delete triggers on those
rows. But that may change in a future release.
The algorithm specified in the OR clause of a COPY, INSERT, or UPDATE
overrides any algorithm specified in a CREATE TABLE or CREATE INDEX. If no
algorithm is specified anywhere, the ABORT algorithm is used.
--------------------------------------------------------------------------
REINDEX
sql-statement ::= REINDEX collation name
sql-statement ::= REINDEX [database-name .]
table/index-name
The REINDEX command is used to delete and recreate indices from scratch.
This is primarily useful when the definition of a collation sequence has
changed.
In the first form, all indices in all attached databases that use the
named collation sequence are recreated. In the second form, if
[database-name.]table/index-name identifies a table, then all indices
associated with the table are rebuilt. If an index is identified, then
only this specific index is deleted and recreated.
If no database-name is specified and there exists both a table or index
and a collation sequence of the specified name, then indices associated
with the collation sequence only are reconstructed. This ambiguity may be
dispelled by always specifying a database-name when reindexing a specific
table or index.
--------------------------------------------------------------------------
REPLACE
sql-statement ::= REPLACE INTO [database-name .] table-name [(
column-list )] VALUES ( value-list ) |
REPLACE INTO [database-name .] table-name [(
column-list )] select-statement
The REPLACE command is an alias for the "INSERT OR REPLACE" variant of the
INSERT command. This alias is provided for compatibility with MySQL. See
the INSERT command documentation for additional information.
--------------------------------------------------------------------------
SELECT
sql-statement ::= SELECT [ALL | DISTINCT] result [FROM table-list]
[WHERE expr]
[GROUP BY expr-list]
[HAVING expr]
[compound-op select]*
[ORDER BY sort-expr-list]
[LIMIT integer [( OFFSET | , ) integer]]
result ::= result-column [, result-column]*
result-column ::= * | table-name . * | expr [ [AS] string ]
table-list ::= table [join-op table join-args]*
table ::= table-name [AS alias] |
( select ) [AS alias]
join-op ::= , | [NATURAL] [LEFT | RIGHT | FULL] [OUTER |
INNER | CROSS] JOIN
join-args ::= [ON expr] [USING ( id-list )]
sort-expr-list ::= expr [sort-order] [, expr [sort-order]]*
sort-order ::= [ COLLATE collation-name ] [ ASC | DESC ]
compound_op ::= UNION | UNION ALL | INTERSECT | EXCEPT
The SELECT statement is used to query the database. The result of a SELECT
is zero or more rows of data where each row has a fixed number of columns.
The number of columns in the result is specified by the expression list in
between the SELECT and FROM keywords. Any arbitrary expression can be used
as a result. If a result expression is * then all columns of all tables
are substituted for that one expression. If the expression is the name of
a table followed by .* then the result is all columns in that one table.
The DISTINCT keyword causes a subset of result rows to be returned, in
which each result row is different. NULL values are not treated as
distinct from each other. The default behavior is that all result rows be
returned, which can be made explicit with the keyword ALL.
The query is executed against one or more tables specified after the FROM
keyword. If multiple tables names are separated by commas, then the query
is against the cross join of the various tables. The full SQL-92 join
syntax can also be used to specify joins. A sub-query in parentheses may
be substituted for any table name in the FROM clause. The entire FROM
clause may be omitted, in which case the result is a single row consisting
of the values of the expression list.
The WHERE clause can be used to limit the number of rows over which the
query operates.
The GROUP BY clauses causes one or more rows of the result to be combined
into a single row of output. This is especially useful when the result
contains aggregate functions. The expressions in the GROUP BY clause do
not have to be expressions that appear in the result. The HAVING clause is
similar to WHERE except that HAVING applies after grouping has occurred.
The HAVING expression may refer to values, even aggregate functions, that
are not in the result.
The ORDER BY clause causes the output rows to be sorted. The argument to
ORDER BY is a list of expressions that are used as the key for the sort.
The expressions do not have to be part of the result for a simple SELECT,
but in a compound SELECT each sort expression must exactly match one of
the result columns. Each sort expression may be optionally followed by a
COLLATE keyword and the name of a collating function used for ordering
text and/or keywords ASC or DESC to specify the sort order.
The LIMIT clause places an upper bound on the number of rows returned in
the result. A negative LIMIT indicates no upper bound. The optional OFFSET
following LIMIT specifies how many rows to skip at the beginning of the
result set. In a compound query, the LIMIT clause may only appear on the
final SELECT statement. The limit is applied to the entire query not to
the individual SELECT statement to which it is attached. Note that if the
OFFSET keyword is used in the LIMIT clause, then the limit is the first
number and the offset is the second number. If a comma is used instead of
the OFFSET keyword, then the offset is the first number and the limit is
the second number. This seeming contradition is intentional - it maximizes
compatibility with legacy SQL database systems.
A compound SELECT is formed from two or more simple SELECTs connected by
one of the operators UNION, UNION ALL, INTERSECT, or EXCEPT. In a compound
SELECT, all the constituent SELECTs must specify the same number of result
columns. There may be only a single ORDER BY clause at the end of the
compound SELECT. The UNION and UNION ALL operators combine the results of
the SELECTs to the right and left into a single big table. The difference
is that in UNION all result rows are distinct where in UNION ALL there may
be duplicates. The INTERSECT operator takes the intersection of the
results of the left and right SELECTs. EXCEPT takes the result of left
SELECT after removing the results of the right SELECT. When three are more
SELECTs are connected into a compound, they group from left to right.
--------------------------------------------------------------------------
UPDATE
sql-statement ::= UPDATE [ OR conflict-algorithm ] [database-name .]
table-name
SET assignment [, assignment]*
[WHERE expr]
assignment ::= column-name = expr
The UPDATE statement is used to change the value of columns in selected
rows of a table. Each assignment in an UPDATE specifies a column name to
the left of the equals sign and an arbitrary expression to the right. The
expressions may use the values of other columns. All expressions are
evaluated before any assignments are made. A WHERE clause can be used to
restrict which rows are updated.
The optional conflict-clause allows the specification of an alternative
constraint conflict resolution algorithm to use during this one command.
See the section titled ON CONFLICT for additional information.
--------------------------------------------------------------------------
VACUUM
sql-statement ::= VACUUM [index-or-table-name]
The VACUUM command is an SQLite extension modeled after a similar command
found in PostgreSQL. If VACUUM is invoked with the name of a table or
index then it is suppose to clean up the named table or index. In version
1.0 of SQLite, the VACUUM command would invoke gdbm_reorganize() to clean
up the backend database file.
VACUUM became a no-op when the GDBM backend was removed from SQLITE in
version 2.0.0. VACUUM was reimplemented in version 2.8.1. The index or
table name argument is now ignored.
When an object (table, index, or trigger) is dropped from the database, it
leaves behind empty space. This makes the database file larger than it
needs to be, but can speed up inserts. In time inserts and deletes can
leave the database file structure fragmented, which slows down disk access
to the database contents. The VACUUM command cleans the main database by
copying its contents to a temporary database file and reloading the
original database file from the copy. This eliminates free pages, aligns
table data to be contiguous, and otherwise cleans up the database file
structure. It is not possible to perform the same process on an attached
database file.
This command will fail if there is an active transaction. This command has
no effect on an in-memory database.
As of SQLite version 3.1, an alternative to using the VACUUM command is
auto-vacuum mode, enabled using the auto_vacuum pragma.
--------------------------------------------------------------------------
PRAGMA
The PRAGMA command is a special command used to modify the operation of
the SQLite library or to query the library for internal (non-table) data.
The PRAGMA command is issued using the same interface as other SQLite
commands (e.g. SELECT, INSERT) but is different in the following important
respects:
* Specific pragma statements may be removed and others added in future
releases of SQLite. Use with caution!
* No error messages are generated if an unknown pragma is issued. Unknown
pragmas are simply ignored. This means if there is a typo in a pragma
statement the library does not inform the user of the fact.
* Some pragmas take effect during the SQL compilation stage, not the
execution stage. This means if using the C-language sqlite3_compile(),
sqlite3_step(), sqlite3_finalize() API (or similar in a wrapper
interface), the pragma may be applied to the library during the
sqlite3_compile() call.
* The pragma command is unlikely to be compatible with any other SQL
engine.
The available pragmas fall into four basic categories:
* Pragmas used to query the schema of the current database.
* Pragmas used to modify the operation of the SQLite library in some
manner, or to query for the current mode of operation.
* Pragmas used to query or modify the databases two version values, the
schema-version and the user-version.
* Pragmas used to debug the library and verify that database files are not
corrupted.
--------------------------------------------------------------------------
PRAGMA command syntax
sql-statement ::= PRAGMA name [= value]
|
PRAGMA function(arg)
The pragmas that take an integer value also accept symbolic names. The
strings "on", "true", and "yes" are equivalent to 1. The strings "off",
"false", and "no" are equivalent to 0. These strings are case-
insensitive, and do not require quotes. An unrecognized string will be
treated as 1, and will not generate an error. When the value is returned
it is as an integer.
--------------------------------------------------------------------------
Pragmas to modify library operation
* PRAGMA auto_vacuum;
PRAGMA auto_vacuum = 0 | 1;
Query or set the auto-vacuum flag in the database.
Normally, when a transaction that deletes data from a database is
committed, the database file remains the same size. Unused database file
pages are marked as such and reused later on, when data is inserted into
the database. In this mode the VACUUM command is used to reclaim unused
space.
When the auto-vacuum flag is set, the database file shrinks when a
transaction that deletes data is committed (The VACUUM command is not
useful in a database with the auto-vacuum flag set). To support this
functionality the database stores extra information internally,
resulting in slightly larger database files than would otherwise be
possible.
It is only possible to modify the value of the auto-vacuum flag before
any tables have been created in the database. No error message is
returned if an attempt to modify the auto-vacuum flag is made after one
or more tables have been created.
* PRAGMA cache_size;
PRAGMA cache_size = Number-of-pages;
Query or change the maximum number of database disk pages that SQLite
will hold in memory at once. Each page uses about 1.5K of memory. The
default cache size is 2000. If you are doing UPDATEs or DELETEs that
change many rows of a database and you do not mind if SQLite uses more
memory, you can increase the cache size for a possible speed
improvement.
When you change the cache size using the cache_size pragma, the change
only endures for the current session. The cache size reverts to the
default value when the database is closed and reopened. Use the
default_cache_size pragma to check the cache size permanently.
* PRAGMA count_changes;
PRAGMA count_changes = 0 | 1;
Query or change the count-changes flag. Normally, when the count-changes
flag is not set, INSERT, UPDATE and DELETE statements return no data.
When count-changes is set, each of these commands returns a single row
of data consisting of one integer value - the number of rows inserted,
modified or deleted by the command. The returned change count does not
include any insertions, modifications or deletions performed by
triggers.
* PRAGMA default_cache_size;
PRAGMA default_cache_size = Number-of-pages;
Query or change the maximum number of database disk pages that SQLite
will hold in memory at once. Each page uses 1K on disk and about 1.5K in
memory. This pragma works like the cache_size pragma with the additional
feature that it changes the cache size persistently. With this pragma,
you can set the cache size once and that setting is retained and reused
every time you reopen the database.
* PRAGMA default_synchronous;
This pragma was available in version 2.8 but was removed in version 3.0.
It is a dangerous pragma whose use is discouraged. To help dissuide
users of version 2.8 from employing this pragma, the documentation will
not tell you what it does.
* PRAGMA empty_result_callbacks;
PRAGMA empty_result_callbacks = 0 | 1;
Query or change the empty-result-callbacks flag.
The empty-result-callbacks flag affects the sqlite3_exec API only.
Normally, when the empty-result-callbacks flag is cleared, the callback
function supplied to the sqlite3_exec() call is not invoked for commands
that return zero rows of data. When empty-result-callbacks is set in
this situation, the callback function is invoked exactly once, with the
third parameter set to 0 (NULL). This is to enable programs that use the
sqlite3_exec() API to retrieve column-names even when a query returns no
data.
* PRAGMA encoding;
PRAGMA encoding = "UTF-8";
PRAGMA encoding = "UTF-16";
PRAGMA encoding = "UTF-16le";
PRAGMA encoding = "UTF-16be";
In it's first form, if the main database has already been created, then
this pragma returns the text encoding used by the main database, one of
"UTF-8", "UTF-16le" (little-endian UTF-16 encoding) or "UTF-16be"
(big-endian UTF-16 encoding). If the main database has not already been
created, then the value returned is the text encoding that will be used
to create the main database, if it is created by this session.
The second and subsequent forms of this pragma are only useful if the
main database has not already been created. In this case the pragma sets
the encoding that the main database will be created with if it is
created by this session. The string "UTF-16" is interpreted as "UTF-16
encoding using native machine byte-ordering".
Databases created by the ATTACH command always use the same encoding as
the main database.
* PRAGMA full_column_names;
PRAGMA full_column_names = 0 | 1;
Query or change the full-column-names flag. This flag affects the way
SQLite names columns of data returned by SELECT statements when the
expression for the column is a table-column name or the wildcard "*".
Normally, such result columns are named <table-name/alias><column-name>
if the SELECT statement joins two or more tables together, or simply
<column-name> if the SELECT statement queries a single table. When the
full-column-names flag is set, such columns are always named
<table-name/alias> <column-name> regardless of whether or not a join is
performed.
If both the short-column-names and full-column-names are set, then the
behaviour associated with the full-column-names flag is exhibited.
* PRAGMA page_size;
PRAGMA page_size = bytes;
Query or set the page-size of the database. The page-size may only be
set if the database has not yet been created. The page size must be a
power of two greater than or equal to 512 and less than or equal to
8192. The upper limit may be modified by setting the value of macro
SQLITE_MAX_PAGE_SIZE during compilation.
* PRAGMA short_column_names;
PRAGMA short_column_names = 0 | 1;
Query or change the short-column-names flag. This flag affects the way
SQLite names columns of data returned by SELECT statements when the
expression for the column is a table-column name or the wildcard "*".
Normally, such result columns are named
<table-name/alias>lt;column-name> if the SELECT statement joins two or
more tables together, or simply <column-name> if the SELECT statement
queries a single table. When the short-column-names flag is set, such
columns are always named <column-name> regardless of whether or not a
join is performed.
If both the short-column-names and full-column-names are set, then the
behaviour associated with the full-column-names flag is exhibited.
* PRAGMA synchronous;
PRAGMA synchronous = FULL; (2)
PRAGMA synchronous = NORMAL; (1)
PRAGMA synchronous = OFF; (0)
Query or change the setting of the "synchronous" flag. The first (query)
form will return the setting as an integer. When synchronous is FULL
(2), the SQLite database engine will pause at critical moments to make
sure that data has actually been written to the disk surface before
continuing. This ensures that if the operating system crashes or if
there is a power failure, the database will be uncorrupted after
rebooting. FULL synchronous is very safe, but it is also slow. When
synchronous is NORMAL (1, the default), the SQLite database engine will
still pause at the most critical moments, but less often than in FULL
mode. There is a very small (though non-zero) chance that a power
failure at just the wrong time could corrupt the database in NORMAL
mode. But in practice, you are more likely to suffer a catastrophic disk
failure or some other unrecoverable hardware fault. So NORMAL is the
default mode. With synchronous OFF (0), SQLite continues without pausing
as soon as it has handed data off to the operating system. If the
application running SQLite crashes, the data will be safe, but the
database might become corrupted if the operating system crashes or the
computer loses power before that data has been written to the disk
surface. On the other hand, some operations are as much as 50 or more
times faster with synchronous OFF.
* PRAGMA temp_store;
PRAGMA temp_store = DEFAULT; (0)
PRAGMA temp_store = FILE; (1)
PRAGMA temp_store = MEMORY; (2)
Query or change the setting of the "temp_store" parameter. When
temp_store is DEFAULT (0), the compile-time C preprocessor macro
TEMP_STORE is used to determine where temporary tables and indices are
stored. When temp_store is MEMORY (2) temporary tables and indices are
kept in memory. When temp_store is FILE (1) temporary tables and indices
are stored in a file. The temp_store_directory pragma can be used to
specify the directory containing this file. FILE is specified. When the
temp_store setting is changed, all existing temporary tables, indices,
triggers, and views are immediately deleted.
It is possible for the library compile-time C preprocessor symbol
TEMP_STORE to override this pragma setting. The following table
summarizes the interaction of the TEMP_STORE preprocessor macro and the
temp_store pragma:
+---------------------------------------------+
| | PRAGMA | Storage used for |
|TEMP_STORE|temp_store|TEMP tables and indices|
|----------+----------+-----------------------|
| 0 | any | file |
|----------+----------+-----------------------|
| 1 | 0 | file |
|----------+----------+-----------------------|
| 1 | 1 | file |
|----------+----------+-----------------------|
| 1 | 2 | memory |
|----------+----------+-----------------------|
| 2 | 0 | memory |
|----------+----------+-----------------------|
| 2 | 1 | file |
|----------+----------+-----------------------|
| 2 | 2 | memory |
|----------+----------+-----------------------|
| 3 | any | memory |
+---------------------------------------------+
* PRAGMA temp_store_directory;
PRAGMA temp_store_directory = 'directory-name';
Query or change the setting of the "temp_store_directory" - the
directory where files used for storing temporary tables and indices are
kept. This setting lasts for the duration of the current connection only
and resets to its default value for each new connection opened.
When the temp_store_directory setting is changed, all existing temporary
tables, indices, triggers, and viewers are immediately deleted. In
practice, temp_store_directory should be set immediately after the
database is opened.
The value directory-name should be enclosed in single quotes. To revert
the directory to the default, set the directory-name to an empty string,
e.g., PRAGMA temp_store_directory = ''. An error is raised if
directory-name is not found or is not writable.
The default directory for temporary files depends on the OS. For
Unix/Linux/OSX, the default is the is the first writable directory found
in the list of: /var/tmp, /usr/tmp, /tmp, and current-directory. For
Windows NT, the default directory is determined by Windows, generally
C:\Documents and Settings\user-name\Local Settings\Temp\. Temporary
files created by SQLite are unlinked immediately after opening, so that
the operating system can automatically delete the files when the SQLite
process exits. Thus, temporary files are not normally visible through ls
or dir commands.
--------------------------------------------------------------------------
Pragmas to query the database schema
* PRAGMA database_list;
For each open database, invoke the callback function once with
information about that database. Arguments include the index and the
name the database was attached with. The first row will be for the main
database. The second row will be for the database used to store
temporary tables.
* PRAGMA foreign_key_list(table-name);
For each foreign key that references a column in the argument table,
invoke the callback function with information about that foreign key.
The callback function will be invoked once for each column in each
foreign key.
* PRAGMA index_info(index-name);
For each column that the named index references, invoke the callback
function once with information about that column, including the column
name, and the column number.
* PRAGMA index_list(table-name);
For each index on the named table, invoke the callback function once
with information about that index. Arguments include the index name and
a flag to indicate whether or not the index must be unique.
* PRAGMA table_info(table-name);
For each column in the named table, invoke the callback function once
with information about that column, including the column name, data
type, whether or not the column can be NULL, and the default value for
the column.
--------------------------------------------------------------------------
Pragmas to query/modify version values
* PRAGMA [database.]schema_version;
PRAGMA [database.]schema_version = integer ;
PRAGMA [database.]user_version;
PRAGMA [database.]user_version = integer ;
The pragmas schema_version and user_version are used to set or get the
value of the schema-version and user-version, respectively. Both the
schema-version and the user-version are 32-bit signed integers stored in
the database header.
The schema-version is usually only manipulated internally by SQLite. It
is incremented by SQLite whenever the database schema is modified (by
creating or dropping a table or index). The schema version is used by
SQLite each time a query is executed to ensure that the internal cache
of the schema used when compiling the SQL query matches the schema of
the database against which the compiled query is actually executed.
Subverting this mechanism by using "PRAGMA schema_version" to modify the
schema-version is potentially dangerous and may lead to program crashes
or database corruption. Use with caution!
The user-version is not used internally by SQLite. It may be used by
applications for any purpose.
--------------------------------------------------------------------------
Pragmas to debug the library
* PRAGMA integrity_check;
The command does an integrity check of the entire database. It looks for
out-of-order records, missing pages, malformed records, and corrupt
indices. If any problems are found, then a single string is returned
which is a description of all problems. If everything is in order, "ok"
is returned.
* PRAGMA parser_trace = ON; (1)
PRAGMA parser_trace = OFF; (0)
Turn tracing of the SQL parser inside of the SQLite library on and off.
This is used for debugging. This only works if the library is compiled
without the NDEBUG macro.
* PRAGMA vdbe_trace = ON; (1)
PRAGMA vdbe_trace = OFF; (0)
Turn tracing of the virtual database engine inside of the SQLite library
on and off. This is used for debugging. See the VDBE documentation for
more information.
* PRAGMA vdbe_listing = ON; (1)
PRAGMA vdbe_listing = OFF; (0)
Turn listings of virtual machine programs on and off. With listing is
on, the entire content of a program is printed just prior to beginning
execution. This is like automatically executing an EXPLAIN prior to each
statement. The statement executes normally after the listing is printed.
This is used for debugging. See the VDBE documentation for more
information.
--------------------------------------------------------------------------
SQLite keywords
The SQL standard specifies a huge number of keywords which may not be used
as the names of tables, indices, columns, or databases. The list is so
long that few people can remember them all. For most SQL code, your safest
bet is to never use any English language word as the name of a
user-defined object.
If you want to use a keyword as a name, you need to quote it. There are
three ways of quoting keywords in SQLite:
'keyword' A keyword in single quotes is interpreted as a literal string
if it occurs in a context where a string literal is allowed,
otherwise it is understood as an identifier.
"keyword" A keyword in double-quotes is interpreted as an identifier if
it matches a known identifier. Otherwise it is interpreted as
a string literal.
[keyword] A keyword enclosed in square brackets is always understood as
an identifier. This is not standard SQL. This quoting
mechanism is used by MS Access and SQL Server and is included
in SQLite for compatibility.
Quoted keywords are unaesthetic. To help you avoid them, SQLite allows
many keywords to be used unquoted as the names of databases, tables,
indices, triggers, views, and/or columns. In the list of keywords that
follows, those that can be used as identifiers are shown in an italic
font. Keywords that must be quoted in order to be used as identifiers are
shown in bold.
SQLite adds new keywords from time to time when it take on new features.
So to prevent you code from being broken by future enhancements, you
should normally quote any indentifier that is an English language word,
even if you do not have to.
The following are the keywords currently recognized by SQLite:
ABORT CURRENT_DATE FROM MATCH SELECT
AFTER CURRENT_TIME FULL NATURAL SET
ALL CURRENT_TIMESTAMP GLOB NOT STATEMENT
ALTER DATABASE GROUP NOTNULL TABLE
AND DEFAULT HAVING NULL TEMP
AS DEFERRABLE IGNORE OF TEMPORARY
ASC DEFERRED IMMEDIATE OFFSET THEN
ATTACH DELETE IN ON TO
AUTOINCREMENT DESC INDEX OR TRANSACTION
BEFORE DETACH INITIALLY ORDER TRIGGER
BEGIN DISTINCT INNER OUTER UNION
BETWEEN DROP INSERT PRAGMA UNIQUE
BY EACH INSTEAD PRIMARY UPDATE
CASCADE ELSE INTERSECT RAISE USING
CASE END INTO REFERENCES VACUUM
CHECK ESCAPE IS REINDEX VALUES
COLLATE EXCEPT ISNULL RENAME VIEW
COMMIT EXCLUSIVE JOIN REPLACE WHEN
CONFLICT EXPLAIN KEY RESTRICT WHERE
CONSTRAINT FAIL LEFT RIGHT
CREATE FOR LIKE ROLLBACK
CROSS FOREIGN LIMIT ROW
Special names
The following are not keywords in SQLite, but are used as names of system
objects. They can be used as an identifier for a different type of object.
_ROWID_
MAIN
OID
ROWID
SQLITE_MASTER
SQLITE_SEQUENCE
SQLITE_TEMP_MASTER
TEMP
This page last modified on 2005/03/21 01:24:02