How to throw an error in MySql procedure?

What is the mechanism to force the MySQL to throw an error within the stored procedure?

I have a procedure which call s another function:

PREPARE my_cmd FROM @jobcommand;
EXECUTE my_cmd;
DEALLOCATE PREPARE my_cmd;

the job command is:

jobq.exec("Select 1;wfdlk# to simulatte an error");

then:

CREATE PROCEDURE jobq.`exec`(jobID VARCHAR(128),cmd TEXT)
BEGIN
DECLARE result INT DEFAULT 0;  
SELECT sys_exec( CONCAT('echo ',cmd,' |  base64 -d > ', '/tmp/jobq.',jobID,'.sh ; bash /tmp/jobq.',jobID,'.sh &> /tmp/jobq.',jobID)) INTO result; 
IF result>0 THEN 
# call raise_mysql_error(result); 
END IF;
END;

My jobq.exec is always succeeding. Are there way to rise an error? How to implement raise_mysql_error function??

BTW I am using MySQL 5.5.8

t开发者_如何学Gohanks Arman.

Yes, there is: use the SIGNAL keyword.

You may use following stored procedure to emulate error-throwing:

CREATE PROCEDURE `raise`(`errno` BIGINT UNSIGNED, `message` VARCHAR(256))
BEGIN
SIGNAL SQLSTATE
    'ERR0R'
SET
    MESSAGE_TEXT = `message`,
    MYSQL_ERRNO = `errno`;
END

Example:

CALL `raise`(1356, 'My Error Message');