Problems with mysql syntax

Question

I´m trying to create a trigger on MySQL but I´m having a syntax problem, which I was not able to find. If someone more experience could help me it would be great (it´s the first time I use MySQL!)...

The reason why I´m creating this trigger is for deleting all the orphan "labels", which has a many-to-many relation with "service_descriptor" (this two entities are linked by service_labels).

The code I have is:

CREATE TRIGGER `trg_delete_orphan_label` AFTER DELETE 
FOR EACH ROW ON `restdb`.`service_labels`  
  DELETE FROM `restdb`.`labels`
   WHERE EXISTS (SELECT *
                   FROM old D 
              LEFT_JOIN `restdb`.`service_labels` SL ON SL.`id_label` = D.`id_label` 
                                                    AND D.`id_service` = SL.`id_service`
                  WHERE SL.`id_label` IS NULL
                        `restdb`.`labels`.`id` = D.SL.`id_label`); 

Thanks in advance !

Answer 1

You have missed AND

Try this code

CREATE TRIGGER `trg_delete_orphan_label` AFTER DELETE FOR EACH ROW ON `restdb`.`service_labels`   
    DELETE 
    FROM 
        `restdb`.`labels` 
    WHERE 
        EXISTS (SELECT 
                    * 
                FROM 
                    old D LEFT_JOIN 
                    `restdb`.`service_labels` SL ON 
                        SL.`id_label` = D.`id_label` AND 
                        D.`id_service` = SL.`id_service` 
                WHERE 
                    SL.`id_label` IS NULL AND
                    `restdb`.`labels`.`id` = D.SL.`id_label`                         
                    );  

Answer 2

There are a couple of problems with your trigger, most notably the placement of "FOR EACH ROW", and the way you are treating OLD like a table, when it's really just a row.

This should work for you:

DROP TRIGGER IF EXISTS `trg_delete_orphan_label`;

CREATE TRIGGER `trg_delete_orphan_label` AFTER DELETE ON `service_labels` 
FOR EACH ROW
    DELETE FROM `labels`
    WHERE `id` = OLD.`id_label`
    AND NOT EXISTS (
        SELECT NULL
        FROM `service_labels` SL 
        WHERE SL.`id_label` = `labels`.`id`                        
    );                     

Answer 3

Thanks everyone ... I´ve finaly solved it because of your help...

In the end the work is:

CREATE TRIGGER trg_delete_orphan_label AFTER DELETE ON restdb.service_descriptor
FOR EACH ROW DELETE FROM restdb.labels WHERE id NOT IN ( SELECT restdb.service_labels.id_label FROM restdb.service_labels );