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MySQL 5.7 Reference Manual

13.6.7.2 DECLARE ... HANDLER Statement

DECLAREhandler_action HANDLER    FORcondition_value [,condition_value] ...statementhandler_action: {    CONTINUE  | EXIT  | UNDO}condition_value: {mysql_error_code  | SQLSTATE [VALUE]sqlstate_value  |condition_name  | SQLWARNING  | NOT FOUND  | SQLEXCEPTION}

TheDECLARE ... HANDLER statement specifies a handler that deals with one or more conditions. If one of these conditions occurs, the specifiedstatement executes.statement can be a simple statement such asSETvar_name =value, or a compound statement written usingBEGIN andEND (seeSection 13.6.1, “BEGIN ... END Compound Statement”).

Handler declarations must appear after variable or condition declarations.

Thehandler_action value indicates what action the handler takes after execution of the handler statement:

CONTINUE: Execution of the current program continues.
EXIT: Execution terminates for theBEGIN ... END compound statement in which the handler is declared. This is true even if the condition occurs in an inner block.
UNDO: Not supported.

Thecondition_value forDECLARE ... HANDLER indicates the specific condition or class of conditions that activates the handler. It can take the following forms:

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, seeServer Error Message Reference.
SQLSTATE [VALUE]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, seeServer Error Message Reference.
condition_name: A condition name previously specified withDECLARE ... CONDITION. A condition name can be associated with a MySQL error code or SQLSTATE value. SeeSection 13.6.7.1, “DECLARE ... CONDITION Statement”.
SQLWARNING: Shorthand for the class of SQLSTATE values that begin with'01'.
```
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 aNOT FOUND condition.
```
DECLARE CONTINUE HANDLER FOR NOT FOUND  BEGIN    -- body of handler  END;
```
For another example, seeSection 13.6.6, “Cursors”. TheNOT FOUND condition also occurs forSELECT ... INTOvar_list statements that retrieve no rows.
SQLEXCEPTION: Shorthand for the class of SQLSTATE values that do not begin with'00','01', or'02'.
```
DECLARE CONTINUE HANDLER FOR SQLEXCEPTION  BEGIN    -- body of handler  END;
```

For information about how the server chooses handlers when a condition occurs, seeSection 13.6.7.6, “Scope Rules for Handlers”.

If a condition occurs for which no handler has been declared, the action taken depends on the condition class:

ForSQLEXCEPTION conditions, the stored program terminates at the statement that raised the condition, as if there were anEXIT handler. 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.
ForSQLWARNING conditions, the program continues executing, as if there were aCONTINUE handler.
ForNOT FOUND conditions, if the condition was raised normally, the action isCONTINUE. If it was raised bySIGNAL orRESIGNAL, the action isEXIT.

The following example uses a handler forSQLSTATE '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 (0.00 sec)mysql> SELECT @x//    +------+    | @x   |    +------+    | 3    |    +------+    1 row in set (0.00 sec)

Notice that@x is3 after the procedure executes, which shows that execution continued to the end of the procedure after the error occurred. If theDECLARE ... HANDLER statement had not been present, MySQL would have taken the default action (EXIT) after the secondINSERT failed due to thePRIMARY KEY constraint, andSELECT @x would have returned2.

To ignore a condition, declare aCONTINUE handler for it and associate it with an empty block. For example:

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 useITERATE orLEAVE to refer to labels for blocks that enclose the handler declaration. Consider the following example, where theREPEAT block has a label ofretry:

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;

Theretry label is in scope for theIF statement within the block. It is not in scope for theCONTINUE 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 anEXIT handler. If no block cleanup is required, theBEGIN ... END handler 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  BEGINblock cleanup statements  END;
```

To continue execution, set a status variable in aCONTINUE handler that can be checked in the enclosing block to determine whether the handler was invoked. The following example uses the variabledone for 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;

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