CODEWITHSUNDEEP
mysqlsqltriggers
user862010
user862010

Reputation:

Trigger Error , MySQL

Well, I have researched and have not found a solution to the following problem 'SQL Error (1442): Can not update table' messages' in stored function / trigger because it is already used by statement Which invoked this stored function / trigger. `

My trigger is created, only when I run the INSERT on the table of messages, this error is thrown, my trigger is 

DELIMITER $$ 
DROP TRIGGER IF EXISTS `onMessage` ;
CREATE TRIGGER `onMessage` BEFORE INSERT ON `messages` FOR EACH ROW 
BEGIN
       UPDATE `users` SET `users`.`messages` = ( `users`.`messages` + 1 ) 
       WHERE `users`.`uid` = NEW.uid ;
       DELETE FROM `messages` WHERE `date` < ( NOW( ) - INTERVAL 1 MINUTE ) ;
END ;
$$
DELIMITER ;

Upvotes: 2

Views: 334

Answers (3)

Korhan Ozturk
Korhan Ozturk

Reputation: 11308

It is not possible to update a table for which the trigger is created in the trigger since Mysql does some locking stuff on that table. Therefore you can't insert/update/delete rows of the same table because then the trigger would called again and again, ending up in a recursion.

If you want to create a trigger on the table which will update itself (perfoming a deletion in this case), make sure you use the NEW.column_name to refer to the row after it’s updated.

Upvotes: 0

perissf
perissf

Reputation: 16273

This is a restriction in the use of triggers.

From the MySql documentations:

Within a stored function or trigger, it is not permitted to modify a table that is already being used (for reading or writing) by the statement that invoked the function or trigger.

Upvotes: 4

gbn
gbn

Reputation: 432180

Correct, for MySQL anyway

You can't write to the table associated with a trigger in that trigger. It generates all manner of inconsistencies, not least because MySQL triggers are processed row-by-row (RBAR)

In this case, I'd use a stored procedure to deal with the INSERT on messages

Upvotes: 2

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