Question

I currently have the following MySQL query, which I would like to include in a trigger, rather than as a separate query. The query updates data in two tables which are joinable:

UPDATE `testing_names` INNER JOIN `purchase_names`
  ON `testing_names`.`fulldomain` = `purchase_names`.`fulldomain`
SET
  `testing_names`.`account_id` = `purchase_names`.`account_id`,
  `purchase_names`.`purchase_status` = 1
WHERE `purchase_names`.`purchase_status` = 0

A row is (separately) inserted into testing_names. This row SHOULD have a corresponding entry in purchase_names. After a row is inserted into testing_names, when my UPDATE query is next run, it will update testing_names.account_id and update purchase_names.purchase_status to effectively mark this task as completed.

It makes sense to run this as part of a trigger, but I haven’t been able to create a trigger that does the job.

So far, I have successfully created a trigger:

DELIMITER $$
  CREATE TRIGGER `my_trigger` AFTER INSERT
    ON testing_names 
      FOR EACH ROW BEGIN
        UPDATE `testing_names` INNER JOIN `purchase_names`
          ON `testing_names`.`fulldomain` = `purchase_names`.`fulldomain`
        SET
          `testing_names`.`account_id` = `purchase_names`.`account_id`,
          `purchase_names`.`purchase_status` = 1
        WHERE `purchase_names`.`purchase_status` = 0;
      END$$
DELIMITER ;

but evidently running a new UPDATE query is not allowed, because upon inserting a row, I get an error: #1442 - Can't update table 'testing_names' in stored function/trigger because it is already used by statement which invoked this stored function/trigger.

Answer 1

Unfortunately, a trigger on a table cannot update the same table.

From MySQL documentation:

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.

Instead, you might be able to complete your update by having the trigger on testing_names update purchase_names and have another trigger on purchase_names update testing_names.