Re: BEFORE INSERT trigger > how to rollback the insertion

[Peter Brawley]

The only way to "cancel" an issued Insert or Update or Delete command is to Rollback the transaction containing the command. MySQL Triggers can't Commit or Rollback; such transaction code has to be outside the actual Insert, Update or Delete logic, ie ...

start transaction
insert (evoking triggers &c)
commit on success or rollback on failure

INSERT IGNORE is designed to solve your problem---the IGNORE keyword tells MySQL not to insert the row if it contains a primary or unique value that exists in the table