Supported SQL syntax

SELECT

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 result column name or expression list between the SELECT and optional FROM keywords.

sql-statement   ::=  SELECT [ALL | DISTINCT] result 
                     [FROM table-list] 
                     [WHERE expr] 
                     [GROUP BY expr-list] 
                     [HAVING expr] 
                     [compound-op select-statement]* 
                     [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 )] 
compound-op     ::=  UNION | UNION ALL | INTERSECT | EXCEPT 
sort-expr-list  ::=  expr [sort-order] [, expr [sort-order]]* 
sort-order      ::=  [COLLATE collation-name] [ASC | DESC] 
collation-name  ::=  BINARY | NOCASE

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 are 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 table names are separated by commas, then the query uses the cross join of the various tables. The JOIN syntax can also be used to specify how tables are joined. The only type of outer join that is supported is LEFT OUTER JOIN. The ON clause expression in join-args must resolve to a boolean value. A subquery in parentheses may be used as a table 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 result expression list.

The WHERE clause is used to limit the number of rows the query retrieves. WHERE clause expressions must resolve to a boolean value. WHERE clause filtering is performed before any grouping, so WHERE clause expressions may not include aggregate functions.

The GROUP BY clause causes one or more rows of the result to be combined into a single row of output. A GROUP BY clause 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 SELECT expression list.

The HAVING clause is like WHERE in that it limits the rows returned by the statement. However, the HAVING clause applies after any grouping specified by a GROUP BY clause has occurred. Consequently, the HAVING expression may refer to values that include aggregate functions. A HAVING clause expression is not required to appear in the SELECT list. Like a WHERE expression, a HAVING expression must resolve to a boolean value.

The ORDER BY clause causes the output rows to be sorted. The sort-expr-list argument to the ORDER BY clause 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 (a SELECT using one of the compound-op operators) each sort expression must exactly match one of the result columns. Each sort expression may be optionally followed by a sort-order clause consisting of the COLLATE keyword and the name of a collation function used for ordering text and/or the keyword ASC or DESC to specify the sort order (ascending or descending). The sort-order can be omitted and the default (ascending order) is used. For a definition of the COLLATE clause and collation functions, see COLLATE.

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 SELECT query, the LIMIT clause may only appear after the final SELECT statement, and the limit is applied to the entire query. Note that if the OFFSET keyword is used in the LIMIT clause, then the limit is the first integer and the offset is the second integer. 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 contradiction is intentional — it maximizes compatibility with legacy SQL database systems.

A compound SELECT is formed from two or more simple SELECT statements connected by one of the operators UNION, UNION ALL, INTERSECT, or EXCEPT. In a compound SELECT, all the constituent SELECT statements must specify the same number of result columns. There can only be a single ORDER BY clause after the final SELECT statement (and before the single LIMIT clause, if one is specified). The UNION and UNION ALL operators combine the results of the preceding and following SELECT statements into a single table. The difference is that in UNION, all result rows are distinct, but in UNION ALL, there may be duplicates. The INTERSECT operator takes the intersection of the results of the preceding and following SELECT statements. EXCEPT takes the result of preceding SELECT after removing the results of the following SELECT. When three or more SELECT statements are connected into a compound, they group from first to last.

For a definition of permitted expressions, see Expressions.

Starting with AIR 2.5, the SQL CAST operator is supported when reading to convert BLOB data to ActionScript ByteArray objects. For example, the following code reads raw data that is not stored in the AMF format and stores it in a ByteArray object:

stmt.text = "SELECT CAST(data AS ByteArray) AS data FROM pictures;"; 
stmt.execute(); 
var result:SQLResult = stmt.getResult(); 
var bytes:ByteArray = result.data[0].data;

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 
                    REPLACE INTO [database-name.] table-name [(column-list)] VALUES (value-list) | 
                    REPLACE INTO [database-name.] table-name [(column-list)] select-statement

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 defined when the table is created, or with NULL if no default value is defined.

The second form of the INSERT statement takes its 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 column-list is not specified, or it must match the number of columns named 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. For a definition of allowable SELECT statements, see SELECT.

The optional conflict-algorithm allows the specification of an alternative constraint conflict resolution algorithm to use during this one command. For an explanation and definition of conflict algorithms, see Special statements and clauses .

The two REPLACE INTO forms of the statement are equivalent to using the standard INSERT [OR conflict-algorithm] form with the REPLACE conflict algorithm (i.e. the INSERT OR REPLACE... form).

The two REPLACE INTO forms of the statement are equivalent to using the standard INSERT [OR conflict-algorithm] form with the REPLACE conflict algorithm (i.e. the INSERT OR REPLACE... form).

UPDATE

The update command changes the existing records in a table.

sql-statement  ::=  UPDATE [database-name.] table-name SET column1=value1, column2=value2,... [WHERE expr]

The command consists of the UPDATE keyword followed by the name of the table in which you want to update the records. After the SET keyword, provide the name of the column and the value to which the column to be changed as a comma-separated list. The WHERE clause expression provides the row or rows in which the records are updated.

DELETE

sql-statement  ::=  DELETE FROM [database-name.] table-name [WHERE expr]

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. The WHERE clause expression must resolve to a boolean value. For a definition of permitted expressions, see Expressions.

CREATE TABLE

sql-statement       ::=  CREATE [TEMP | TEMPORARY] TABLE [IF NOT EXISTS] [database-name.] table-name 
                         ( column-def [, column-def]* [, constraint]* ) 
sql-statement       ::=  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 ) | 
                         DEFAULT default-value | 
                         COLLATE collation-name 
constraint          ::=  PRIMARY KEY ( column-list ) [conflict-clause] | 
                         UNIQUE ( column-list ) [conflict-clause] | 
                         CHECK ( expr ) 
conflict-clause     ::=  ON CONFLICT conflict-algorithm 
conflict-algorithm  ::=  ROLLBACK | ABORT | FAIL | IGNORE | REPLACE 
default-value       ::=  NULL | string | number | CURRENT_TIME | CURRENT_DATE | CURRENT_TIMESTAMP 
sort-order          ::=  ASC | DESC 
collation-name      ::=  BINARY | NOCASE 
column-list         ::=  column-name [, column-name]*

Each column definition is the name of the column followed by the data type for that column, then one or more optional column constraints. The data type for the column restricts what data may be stored in that column. If an attempt is made to store a value in a column with a different data type, the runtime converts the value to the appropriate type if possible, or raises an error. See the Data type support section for additional information.

The NOT NULL column constraint indicates that the column cannot contain NULL values.

A UNIQUE constraint causes an index to be created on the specified column or columns. This index must contain unique keys—no two rows may contain duplicate values or combinations of values for the specified column or columns. A CREATE TABLE statement can have multiple UNIQUE constraints, including multiple columns with a UNIQUE constraint in the column's definition and/or multiple table-level UNIQUE constraints.

A CHECK constraint defines an expression that is evaluated and must be true in order for a row's data to be inserted or updated. The CHECK expression must resolve to a boolean value.

A COLLATE clause in a column definition specifies what text collation function to use when comparing text entries for the column. The BINARY collating function is used by default. For details on the COLLATE clause and collation functions, see COLLATE.

The DEFAULT constraint specifies a default value to use when doing an INSERT. The value may be NULL, a string constant, or a number. The default value may also be one of the special case-independent keywords CURRENT_TIME, CURRENT_DATE or CURRENT_TIMESTAMP. If the value is NULL, a string constant, or a number, it is literally inserted into the column whenever an INSERT statement does not specify a value for the column. If the value is CURRENT_TIME, CURRENT_DATE or CURRENT_TIMESTAMP, then the current UTC date and/or time is inserted into the column. For CURRENT_TIME, the format is HH:MM:SS. For CURRENT_DATE, the format is 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 column or columns. However, if the PRIMARY KEY constraint is on a single column that has the data type INTEGER (or one of its synonyms such as int) then that column is used by the database as the actual primary key for the table. This means that the column may only hold unique integer values. (Note that in many SQLite implementations, only the column type INTEGER causes the column to serve as the internal primary key, but in Adobe AIR synonyms for INTEGER such as int also specify that behavior.)

If a table does not have an INTEGER PRIMARY KEY column, an integer key is automatically generated when a row is inserted. The primary key for a row can always be accessed using one of the special names ROWID, OID, or _ROWID_. These names can be used regardless of whether it is an explicitly declared INTEGER PRIMARY KEY or an internal generated value. However, if the table has an explicit INTEGER PRIMARY KEY, the name of the column in the result data is the actual column name rather than the special name.

An INTEGER PRIMARY KEY column can also include the keyword AUTOINCREMENT. When the AUTOINCREMENT keyword is used, the database automatically generates and inserts a sequentially incremented integer key in the INTEGER PRIMARY KEY column when it executes an INSERT statement that doesn't specify an explicit value for the column.

There can only be one PRIMARY KEY constraint in a CREATE TABLE statement. It can either be part of one column's definition or one single table-level PRIMARY KEY constraint. A primary key column is implicitly NOT NULL.

The optional conflict-clause following many constraints allows the specification of an alternative default constraint conflict resolution algorithm for that constraint. The default is ABORT. Different constraints within the same table may have different default conflict resolution algorithms. If an INSERT or UPDATE statement specifies a different conflict resolution algorithm, that algorithm is used in place of the algorithm specified in the CREATE TABLE statement. See the ON CONFLICT section of Special statements and clauses for additional information.

Additional constraints, such as FOREIGN KEY constraints, do not result in an error but the runtime ignores them.

If the TEMP or TEMPORARY keyword occurs between CREATE and TABLE then the table that is created is only visible within the same database connection (SQLConnection instance). It is automatically deleted when the database connection 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 the optional database-name prefix is specified, then the table is created in a named database (a database that was connected to the SQLConnection instance by calling the attach() method with the specified database name). It is an error to specify both a database-name prefix and the TEMP keyword, unless the database-name prefix is temp. If no database name is specified, and the TEMP keyword is not present, the table is created in the main database (the database that was connected to the SQLConnection instance using the open() or openAsync()method).

There are no arbitrary limits on the number of columns or on the number of constraints in a table. There is also no arbitrary limit on the amount of data in a row.

The CREATE TABLE AS form defines the table as the result set of a query. The names of the table columns are the names of the columns in the result.

If the optional IF NOT EXISTS clause is present and another table with the same name already exists, then the database ignores the CREATE TABLE command.

A table can be removed using the DROP TABLE statement, and limited changes can be made using the ALTER TABLE statement.

ALTER TABLE

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.

sql-statement ::= ALTER TABLE [database-name.] table-name alteration 
alteration    ::= RENAME TO new-table-name 
alteration    ::= ADD [COLUMN] column-def

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 they 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, they are not automatically modified to use the new table name. If a renamed table has associated views or triggers, you must manually drop and recreate the triggers or view definitions using the new table name.

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. The column-def clause may take any of the forms permissible 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, the column must have a default value other than NULL.

The execution time of the ALTER TABLE statement is not affected by the amount of data in the table.

DROP TABLE

sql-statement  ::=  DROP TABLE [IF EXISTS] [database-name.] table-name

By default the DROP TABLE statement does not reduce the size of the database file. Empty space in the database is retained and used in subsequent INSERT operations. To remove free space in the database use the SQLConnection.clean() method. If the autoClean parameter is set to true when the database is initially created, the space is freed automatically.

The optional IF EXISTS clause suppresses the error that would normally result if the table does not exist.

CREATE INDEX

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 whose values are used for the index key.

sql-statement  ::=  CREATE [UNIQUE] INDEX [IF NOT EXISTS] [database-name.] index-name 
                    ON table-name ( column-name [, column-name]* ) 
column-name    ::=  name [COLLATE collation-name] [ASC | DESC]

Each column name can be followed by ASC or DESC keywords to indicate sort order, but the sort order designation is ignored by the runtime. Sorting is always done in ascending order.

The COLLATE clause following each column name defines a collating sequence used for text values in that column. The default collation sequence is the collation sequence defined for that column in the CREATE TABLE statement. If no collation sequence is specified, the BINARY collation sequence is used. For a definition of the COLLATE clause and collation functions see COLLATE.

There are no arbitrary limits on the number of indices that can be attached to a single table. There are also no limits on the number of columns in an index.

DROP INDEX

The drop index statement removes an index added with the CREATE INDEX statement. The specified index is completely removed from the database file. The only way to recover the index is to reenter the appropriate CREATE INDEX command.

sql-statement ::= DROP INDEX [IF EXISTS] [database-name.] index-name

By default the DROP INDEX statement does not reduce the size of the database file. Empty space in the database is retained and used in subsequent INSERT operations. To remove free space in the database use the SQLConnection.clean() method. If the autoClean parameter is set to true when the database is initially created, the space is freed automatically.

CREATE VIEW

The CREATE VIEW command assigns a name to a pre-defined SELECT statement. This new name can then be used in a FROM clause of another SELECT statement in place of a table name. Views are commonly used to simplify queries by combining a complex (and frequently used) set of data into a structure that can be used in other operations.

sql-statement ::= CREATE [TEMP | TEMPORARY] VIEW [IF NOT EXISTS] [database-name.] view-name AS select-statement

If the TEMP or TEMPORARY keyword occurs in between CREATE and VIEW then the view that is created is only visible to the SQLConnection instance that opened the database and is automatically deleted when the database is closed.

If a [database-name] is specified the view is created in the named database (a database that was connected to the SQLConnection instance using the attach() method, with the specified name argument. 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 view is created in the main database (the database that was connected to the SQLConnection instance using the open() or openAsync() method).

Views are read only. A DELETE, INSERT, or UPDATE statement cannot be used on a view, unless at least one trigger of the associated type (INSTEAD OF DELETE, INSTEAD OF INSERT, INSTEAD OF UPDATE) is defined. For information on creating a trigger for a view, see CREATE TRIGGER.

A view is removed from a database using the DROP VIEW statement.

DROP VIEW

The DROP VIEW statement removes a view created by a CREATE VIEW statement.

sql-statement ::= DROP VIEW [IF EXISTS] view-name

The specified view-name is the name of the view to drop. It is removed from the database, but no data in the underlying tables is modified.

CREATE TRIGGER

The create trigger statement is used to add triggers to the database schema. A trigger is a database operation (the trigger-action) that is automatically performed when a specified database event (the database-event) occurs.

sql-statement   ::=  CREATE [TEMP | TEMPORARY] TRIGGER [IF NOT EXISTS] [database-name.] trigger-name 
                     [BEFORE | AFTER] database-event 
                     ON table-name 
                     trigger-action 
sql-statement   ::=  CREATE [TEMP | TEMPORARY] TRIGGER [IF NOT EXISTS] [database-name.] trigger-name 
                     INSTEAD OF database-event 
                     ON view-name 
                     trigger-action 
database-event  ::=  DELETE | 
                     INSERT | 
                     UPDATE | 
                     UPDATE OF column-list 
trigger-action  ::=  [FOR EACH ROW] [WHEN expr] 
                     BEGIN 
                       trigger-step ; 
                       [ trigger-step ; ]* 
                     END 
trigger-step    ::=  update-statement | 
                     insert-statement | 
                     delete-statement | 
                     select-statement 
column-list     ::=  column-name [, column-name]*

A trigger is 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. Triggers are permanent unless the TEMP or TEMPORARY keyword is used. In that case the trigger is removed when the SQLConnection instance's main database connection is closed. If no timing is specified (BEFORE or AFTER) the trigger defaults to BEFORE.

Only FOR EACH ROW triggers are supported, so the FOR EACH ROW text is optional. With a FOR EACH ROW trigger, the trigger-step statements are executed for each database row being inserted, updated or deleted by the statement causing the trigger to fire, if the WHEN clause expression evaluates to true.

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.

Within the body of a trigger, (the trigger-action clause) the pre-change and post-change values of the affected table are available using the special table names OLD and NEW. The structure of the OLD and NEW tables matches the structure of the table on which the trigger is created. The OLD table contains any rows that are modified or deleted by the triggering statement, in their state before the triggering statement's operations. The NEW table contains any rows that are modified or created by the triggering statement, in their state after the triggering statement's operations. Both the WHEN clause and the trigger-step statements can access values from 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 with which the trigger is associated. The availability of the OLD and NEW table references depends on the type of database-event the trigger handles:

• INSERT – NEW references are valid

• UPDATE – NEW and OLD references are valid

• DELETE – OLD references are valid

The specified timing (BEFORE, AFTER, or INSTEAD OF) determines when the trigger-step statements are 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 statement in a trigger-step. However, if an ON CONFLICT clause is specified as part of the statement causing the trigger to fire, then that conflict handling policy is used instead.

In addition to table triggers, an INSTEAD OF trigger can be created on a view. If one or more INSTEAD OF INSERT, INSTEAD OF DELETE, or INSTEAD OF UPDATE triggers are defined on a view, it is not considered an error to execute the associated type of statement (INSERT, DELETE, or UPDATE) on the view. In that case, executing an INSERT, DELETE or UPDATE on the view causes the associated triggers to fire. Because the trigger is an INSTEAD OF trigger, the tables underlying the view are not modified by the statement that causes the trigger to fire. However, the triggers can be used to perform modifying operations on the underlying tables.

There is an important issue to keep in mind when creating a trigger on a table with an INTEGER PRIMARY KEY column. If a BEFORE trigger modifies the INTEGER PRIMARY KEY column of a row that is to be updated by the statement that causes the trigger to fire, the update doesn't occur. A workaround is to create the table with a PRIMARY KEY column instead of an INTEGER PRIMARY KEY column.

A trigger can be removed using the DROP TRIGGER statement. When a table or view is dropped, all triggers associated with that table or view are automatically dropped as well.

RAISE () function

A special SQL function RAISE() can be used in a trigger-step statement of a trigger. This function has 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 execution, the specified ON CONFLICT processing action (ABORT, FAIL, or ROLLBACK) is performed and the current statement's execution ends. The ROLLBACK is considered a statement execution failure, so the SQLStatement instance whose execute() method was being carried out dispatches an error (SQLErrorEvent.ERROR) event. The SQLError object in the dispatched event object's error property has its details property set to the error-message specified in the RAISE() function.

When RAISE(IGNORE) is called, the remainder of the current trigger, the statement that caused the trigger to execute, and any subsequent triggers that would have been executed are abandoned. No database changes are rolled back. If the statement that caused the trigger to execute is itself part of a trigger, that trigger program resumes execution at the beginning of the next step. For more information about the conflict resolution algorithms, see the section ON CONFLICT (conflict algorithms).

DROP TRIGGER

The DROP TRIGGER statement removes a trigger created by the CREATE TRIGGER statement.

sql-statement  ::=  DROP TRIGGER [IF EXISTS] [database-name.] trigger-name

The trigger is deleted from the database. Note that triggers are automatically dropped when their associated table is dropped.

COLLATE

The COLLATE clause is used in SELECT, CREATE TABLE, and CREATE INDEX statements to specify the comparison algorithm that is used when comparing or sorting values.

sql-statement   ::=  COLLATE collation-name 
collation-name  ::=  BINARY | NOCASE

The default collation type for columns is BINARY. When BINARY collation is used with values of the TEXT storage class, binary collation is performed by comparing the bytes in memory that represent the value regardless of the text encoding.

The NOCASE collation sequence is only applied for values of the TEXT storage class. When used, the NOCASE collation performs a case-insensitive comparison.

No collation sequence is used for storage classes of type NULL, BLOB, INTEGER, or REAL.

To use a collation type other than BINARY with a column, a COLLATE clause must be specified as part of the column definition in the CREATE TABLE statement. Whenever two TEXT values are compared, a collation sequence is used to determine the results of the comparison according to the following rules:

EXPLAIN

The EXPLAIN command modifier is a non-standard extension to SQL.

sql-statement  ::=  EXPLAIN sql-statement

If the EXPLAIN keyword appears before any other SQL statement, then instead of actually executing the command, the result reports the sequence of virtual machine instructions it would have used to execute the command, had the EXPLAIN keyword not been present. The EXPLAIN feature is an advanced feature and allows developers to change SQL statement text in an attempt to optimize performance or debug a statement that doesn't appear to be working properly.

ON CONFLICT (conflict algorithms)

The ON CONFLICT clause is not a separate SQL command. It is a non-standard clause that can appear in many other SQL commands.

conflict-clause     ::=  ON CONFLICT conflict-algorithm 
conflict-clause     ::=  OR conflict-algorithm 
conflict-algorithm  ::=  ROLLBACK | 
                         ABORT | 
                         FAIL | 
                         IGNORE | 
                         REPLACE

The first form of the ON CONFLICT clause, using the keywords ON CONFLICT, is used in a CREATE TABLE statement. For an INSERT or UPDATE statement, the second form is used, with ON CONFLICT replaced by OR to make the syntax seem more natural. For example, instead of INSERT ON CONFLICT IGNORE, the statement becomes INSERT OR IGNORE. Although the keywords are different, the meaning of the clause is the same in either form.

The ON CONFLICT clause specifies the algorithm that is used to resolve constraint conflicts. The five algorithms are ROLLBACK, ABORT, FAIL, IGNORE, and REPLACE. The default algorithm is ABORT. The following is an explanation of the five conflict algorithms:

ROLLBACK

When a constraint violation occurs, an immediate ROLLBACK occurs, ending the current transaction. The command aborts and the SQLStatement instance dispatches an error event. 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 the SQLStatement instance dispatches an error event. No ROLLBACK is executed, so changes from prior commands within a transaction are preserved. ABORT is the default behavior.

FAIL

When a constraint violation occurs, the command aborts and the SQLStatement dispatches an error event. However, any changes to the database that the statement made before encountering the constraint violation are preserved and are not backed out. For example, if an UPDATE statement encounters 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 don’t occur.

IGNORE

When a constraint violation occurs, the one row that contains the constraint violation is not inserted or changed. Aside from this row being ignored, 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 before inserting or updating the current row. Consequently, the insert or update always occurs, and 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. If a CHECK constraint violation occurs then the IGNORE 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.

The algorithm specified in the OR clause of an INSERT or UPDATE statement overrides any algorithm specified in a CREATE TABLE statement. If no algorithm is specified in the CREATE TABLE statement or the executing INSERT or UPDATE statement, the ABORT algorithm is used.

REINDEX

The REINDEX command is used to delete and re-create one or more indices. This command is useful when the definition of a collation sequence has changed.

sql-statement  ::=  REINDEX collation-name 
sql-statement  ::=  REINDEX [database-name .] ( table-name | index-name )

In the first form, all indices in all attached databases that use the named collation sequence are recreated. In the second form, when a table-name is specified, all indices associated with the table are rebuilt. If an index-name is given, only the specified index is deleted and recreated.

COMMENTS

Comments aren't SQL commands, but they can occur in SQL queries. They are treated as white space by the runtime. They can begin anywhere white space can be found, including inside expressions that span multiple lines.

comment             ::=  single-line-comment | 
                         block-comment 
single-line-comment ::=  -- single-line 
block-comment       ::=  /* multiple-lines or block [*/]

A single-line comment is indicated by two dashes. A single line comment only extends to the end of the current line.

Block comments can span any number of lines, or be embedded within a single line. If there is no terminating delimiter, a block comment extends to the end of the input. This situation is not treated as an error. A new SQL statement can begin on a line after a block comment ends. Block comments can be embedded anywhere white space can occur, including inside expressions, and in the middle of other SQL statements. Block comments do not nest. Single-line comments inside a block comment are ignored.

EXPRESSIONS

Expressions are subcommands within other SQL blocks. The following describes the valid syntax for an expression within a SQL statement:

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 
binary-op       ::=  see Operators 
unary-op        ::=  see Operators 
parameter       ::=  :param-name | @param-name | ? 
value-list      ::=  literal-value [, literal-value]* 
literal-value   ::=  literal-string | literal-number | literal-boolean | literal-blob | literal-null 
literal-string  ::=  'string value' 
literal-number  ::=  integer | number 
literal-boolean  ::=  true | false 
literal-blob  ::=  X'string of hexadecimal data' 
literal-null  ::=  NULL

An expression is any combination of values and operators that can be resolved to a single value. Expressions can be divided into two general types, according to whether they resolve to a boolean (true or false) value or whether they resolve to a non-boolean value.

In several common situations, including in a WHERE clause, a HAVING clause, the ON expression in a JOIN clause, and a CHECK expression, the expression must resolve to a boolean value. The following types of expressions meet this condition:

• ISNULL

• NOTNULL

• IN () �

• EXISTS ()

• LIKE

• GLOB

• Certain functions

• Certain operators (specifically comparison operators)

Literal values

A literal numeric value is written as an integer number or a floating point number. Scientific notation is supported. The . (period) character is always used as the decimal point.

A string literal is indicated by enclosing the string in single quotes '. To include a single quote within a string, put two single quotes in a row like this example: ''.

A boolean literal is indicated by the value true or false. Literal boolean values are used with the Boolean column data type.

A BLOB literal is a string literal containing hexadecimal data and proceeded by a single x or X character, such as X'53514697465'.

A literal value can also be the token NULL.

Column name

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 behave as 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. The SELECT * FROM table statement does not include the row key in its result set.

SELECT statement

A SELECT statement can appear in an expression as either the right-hand operand of the IN operator, as a scalar quantity (a single result value), or as the operand of an EXISTS operator. When used as a scalar quantity or the operand of an IN operator, the SELECT can only have a single column in its result. A compound SELECT statement (connected with keywords like UNION or EXCEPT) is 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 the value in the containing query, then the expression is evaluated once before any other processing and the result is reused as necessary. If the SELECT expression does contain variables from the outer query, known as a correlated subquery, then the SELECT is re-evaluated 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 equal to any of the values in the SELECT statement's result set. 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.

CAST expression

A CAST expression changes the data type of the value specified to the one given. The type specified can be any non-empty type name that is valid for the type in a column definition of a CREATE TABLE statement. See Data type support for details.

Additional expression elements

The following SQL elements can also be used in expressions:

• Built-in functions: Aggregate functions, Scalar functions, and Date and time formatting functions

• Operators

• Parameters

Aggregate functions

Aggregate functions perform operations on values from multiple rows. These functions are primarily used in SELECT statements in conjunction with the GROUP BY clause.

In any of the preceding aggregate functions that take a single argument, that argument can be preceded by the keyword DISTINCT. In that case, duplicate elements are filtered before being passed into the aggregate function. For example, the function call COUNT(DISTINCT x) returns the number of distinct values of column X instead of the total number of non-NULL values in column x.

Scalar functions

Scalar functions operate on values one row at a time.

Date and time formatting functions

The date and time formatting functions are a group of scalar functions that are used to create formatted date and time data. Note that these functions operate on and return string and number values. These functions are not intended to be used with the DATE data type. If you use these functions on data in a column whose declared data type is DATE, they do not behave as expected.

Time formats

The character T in these formats is a literal character "T" separating the date and the time. Formats that only include a time assume the date 2001-01-01.

Modifiers

Common operators

The following binary operators are allowed in a SQL block and are listed in order from highest to lowest precedence:

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

Supported unary prefix operators are:

 !    ~    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.

Note that there are two variations of the equals and not equals operators. Equals can be either = or ==. The not-equals operator can be either != or <>.

The || operator is the string concatenation operator—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.

SQL operators

LIKE

The LIKE operator does a pattern matching comparison.

expr     ::=  (column-name | expr) LIKE pattern 
pattern  ::=  '[ string | % | _ ]'

The operand to the right of the LIKE operator contains the pattern, and the left-hand operand contains the string to match against the pattern. A percent symbol (%) in the pattern is a wildcard character—it 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 its lower/upper case equivalent, that is, matches are performed in a case-insensitive manner. (Note: the database engine only understands upper/lower case for 7-bit Latin characters. Consequently, 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). Case sensitivity for Latin characters can be changed using the SQLConnection.caseSensitiveLike property.

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 match 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.

GLOB

The GLOB operator is similar to LIKE but uses the Unix file globbing syntax for its wildcards. Unlike LIKE, GLOB is case sensitive.

IN

The IN operator calculates whether its left operand is equal to one of the values in its right operand (a set of values in parentheses).

in-expr         ::=  expr [NOT] IN ( value-list ) | 
                     expr [NOT] IN ( select-statement ) | 
                     expr [NOT] IN [database-name.] table-name 
value-list      ::=  literal-value [, literal-value]*

The right operand can be a set of comma-separated literal values, or it can be the result of a SELECT statement. See SELECT statements in expressions for an explanation and limitations on using a SELECT statement as the right-hand operand of the IN operator.

BETWEEN...AND

The BETWEEN...AND operator is equivalent to using two expressions with the >= and <= operators. For example, the expression x BETWEEN y AND z is equivalent to x >= y AND x <= z.

NOT

The NOT operator is a negation operator. The GLOB, LIKE, and IN operators may be preceded by the NOT keyword to invert the sense of the test (in other words, to check that a value does not match the indicated pattern).