DECLARE handler_action HANDLER FOR condition_value [, condition_value] ... statement handler_action: CONTINUE | EXIT | UNDO condition_value: mysql_error_code | SQLSTATE [VALUE] sqlstate_value | condition_name | SQLWARNING | NOT FOUND | SQLEXCEPTION
HANDLER statement specifies a handler that deals with
one or more conditions. If one of these conditions occurs, the
statement can be a simple statement
SET , or a compound
statement written using
END (see Section 13.6.1, “BEGIN ... END Compound-Statement Syntax”).
Handler declarations must appear after variable or condition declarations.
handler_action value indicates
what action the handler takes after execution of the handler
CONTINUE: Execution of the current program continues.
EXIT: Execution terminates for the
BEGIN ... ENDcompound statement in which the handler is declared. This is true even if the condition occurs in an inner block.
UNDO: Not supported.
HANDLER indicates the specific condition or class of
conditions that activates the handler. It can take the following
mysql_error_code: An integer literal indicating a MySQL error code, such as 1051 to specify “unknown table”:
DECLARE CONTINUE HANDLER FOR 1051 BEGIN -- body of handler END;
Do not use MySQL error code 0 because that indicates success rather than an error condition. For a list of MySQL error codes, see Section B.3, “Server Error Codes and Messages”.
sqlstate_value: A 5-character string literal indicating an SQLSTATE value, such as
'42S01'to specify “unknown table”:
DECLARE CONTINUE HANDLER FOR SQLSTATE '42S02' BEGIN -- body of handler END;
Do not use SQLSTATE values that begin with
'00'because those indicate success rather than an error condition. For a list of SQLSTATE values, see Section B.3, “Server Error Codes and Messages”.
condition_name: A condition name previously specified with
DECLARE ... CONDITION. A condition name can be associated with a MySQL error code or SQLSTATE value. See Section 126.96.36.199, “DECLARE ... CONDITION Syntax”.
SQLWARNING: Shorthand for the class of SQLSTATE values that begin with
DECLARE CONTINUE HANDLER FOR SQLWARNING BEGIN -- body of handler END;
NOT FOUND: Shorthand for the class of SQLSTATE values that begin with
'02'. This is relevant within the context of cursors and is used to control what happens when a cursor reaches the end of a data set. If no more rows are available, a No Data condition occurs with SQLSTATE value
'02000'. To detect this condition, you can set up a handler for it or for a
DECLARE CONTINUE HANDLER FOR NOT FOUND BEGIN -- body of handler END;
For another example, see Section 13.6.6, “Cursors”. The
NOT FOUNDcondition also occurs for
SELECT ... INTOstatements that retrieve no rows.
SQLEXCEPTION: Shorthand for the class of SQLSTATE values that do not begin with
DECLARE CONTINUE HANDLER FOR SQLEXCEPTION BEGIN -- body of handler END;
If a condition occurs for which no handler has been declared, the action taken depends on the condition class:
SQLEXCEPTIONconditions, the stored program terminates at the statement that raised the condition, as if there were an
EXIThandler. If the program was called by another stored program, the calling program handles the condition using the handler selection rules applied to its own handlers.
SQLWARNINGconditions, the program continues executing, as if there were a
The following example uses a handler for
'23000', which occurs for a duplicate-key error:
mysql> CREATE TABLE test.t (s1 INT, PRIMARY KEY (s1)); Query OK, 0 rows affected (0.00 sec) mysql> delimiter // mysql> CREATE PROCEDURE handlerdemo () -> BEGIN -> DECLARE CONTINUE HANDLER FOR SQLSTATE '23000' SET @x2 = 1; -> SET @x = 1; -> INSERT INTO test.t VALUES (1); -> SET @x = 2; -> INSERT INTO test.t VALUES (1); -> SET @x = 3; -> END; -> // Query OK, 0 rows affected (0.00 sec) mysql> CALL handlerdemo()// Query OK, 0 rows affected, 1 warning (0.01 sec) mysql> SHOW WARNINGS// +-------+------+---------------------------------------+ | Level | Code | Message | +-------+------+---------------------------------------+ | Error | 1062 | Duplicate entry '1' for key 'PRIMARY' | +-------+------+---------------------------------------+ 1 row in set (0.00 sec) mysql> SELECT @x// +------+ | @x | +------+ | 3 | +------+ 1 row in set (0.00 sec)
the procedure executes, which shows that execution continued to
the end of the procedure after the error occurred. If the
HANDLER statement had not been present, MySQL would
have taken the default action (
INSERT failed due to
PRIMARY KEY constraint, and
SELECT @x would have returned
To ignore a condition, declare a
handler for it and associate it with an empty block. For
DECLARE CONTINUE HANDLER FOR SQLWARNING BEGIN END;
The scope of a block label does not include the code for
handlers declared within the block. Therefore, the statement
associated with a handler cannot use
LEAVE to refer to labels for
blocks that enclose the handler declaration. Consider the
following example, where the
REPEAT block has a label of
CREATE PROCEDURE p () BEGIN DECLARE i INT DEFAULT 3; retry: REPEAT BEGIN DECLARE CONTINUE HANDLER FOR SQLWARNING BEGIN ITERATE retry; # illegal END; IF i < 0 THEN LEAVE retry; # legal END IF; SET i = i - 1; END; UNTIL FALSE END REPEAT; END;
retry label is in scope for the
IF statement within the block. It
is not in scope for the
CONTINUE handler, so
the reference there is invalid and results in an error:
ERROR 1308 (42000): LEAVE with no matching label: retry
To avoid references to outer labels in handlers, use one of these strategies:
To leave the block, use an
EXIThandler. If no block cleanup is required, the
BEGIN ... ENDhandler body can be empty:
DECLARE EXIT HANDLER FOR SQLWARNING BEGIN END;
Otherwise, put the cleanup statements in the handler body:
DECLARE EXIT HANDLER FOR SQLWARNING BEGIN block cleanup statements END;
To continue execution, set a status variable in a
CONTINUEhandler that can be checked in the enclosing block to determine whether the handler was invoked. The following example uses the variable
donefor this purpose:
CREATE PROCEDURE p () BEGIN DECLARE i INT DEFAULT 3; DECLARE done INT DEFAULT FALSE; retry: REPEAT BEGIN DECLARE CONTINUE HANDLER FOR SQLWARNING BEGIN SET done = TRUE; END; IF done OR i < 0 THEN LEAVE retry; END IF; SET i = i - 1; END; UNTIL FALSE END REPEAT; END;