Certain conditions may require specific handling. These conditions can relate to errors, as well as general flow control inside a routine.
DECLARE condition_name CONDITION FOR condition_value condition_value: SQLSTATE [VALUE] sqlstate_value | mysql_error_code
This statement specifies conditions that will need specific handling. It associates a name with a specified error condition. The name can subsequently be used in a DECLARE HANDLER statement. See DECLARE Handlers.
In addition to SQLSTATE values, MySQL error codes are also supported.
DECLARE handler_type HANDLER FOR condition_value[,...] sp_statement handler_type: CONTINUE | EXIT | UNDO condition_value: SQLSTATE [VALUE] sqlstate_value | condition_name | SQLWARNING | NOT FOUND | SQLEXCEPTION | mysql_error_code
This statement specifies handlers that each may deal with one or more conditions. If one of these conditions occurs, the specified statement is executed.
For a CONTINUE handler, execution of the current routine continues after execution of the handler statement. For an EXIT handler, execution of the current routine is terminated. The UNDO handler_type is not yet supported. UNDO currently behaves like CONTINUE.
SQLWARNING is shorthand for all SQLSTATE codes that begin with 01.
NOT FOUND is shorthand for all SQLSTATE codes that begin with 02.
EXCEPTION is shorthand for all SQLSTATE codes not caught by SQLWARNING or NOT FOUND.
In addition to SQLSTATE values, MySQL error codes are also supported.
For example:
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 '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 (0.00 sec) mysql> SELECT @x| +------+ | @x | +------+ | 3 | +------+ 1 row in set (0.00 sec)
Notice that @x is 3, which shows that MySQL executed to the end of the procedure. If the line DECLARE CONTINUE HANDLER FOR '23000' SET @x2 = 1; had not been present, MySQL would have taken the default (EXIT) path after the second INSERT failed due to the PRIMARY KEY constraint, and SELECT @x would have returned 2.