Contents
How to avoid deleting more than one row at a time in MySQL?
I am trying to avoid deletion of more than 1 row at a time in MySQL by using a BEFORE DELETE trigger. The sample table and trigger are as below.
How many rows can I delete at a time?
Deleting 10,000 rows at a time is typically a large enough task to make each query efficient, and a short enough task to minimize the impact on the server4 (transactional storage engines might benefit from smaller transactions).
What happens when I delete a table in MySQL?
The only tricky part here is that the table in question is a reporting table, so once it’s renamed out of the way and the empty one put in its place all historic reports go away until I put it back in place. Plus the merging process could be a bit of a pain because of the type of data being stored.
How to avoid deleting more than one order at a time?
DELIMITER // DROP TRIGGER IF EXISTS prevent_multiple_deletion; CREATE TRIGGER prevent_multiple_deletion BEFORE DELETE ON test FOR EACH STATEMENT BEGIN IF (ROW_COUNT ()>=2) THEN SIGNAL SQLSTATE ‘45000’ SET MESSAGE_TEXT = ‘Cannot delete more than one order per time!’; END IF; END // DELIMITER ;
How does the before delete trigger work in MySQL?
The succeeding BEFORE DELETE trigger will add a new row in the table Salary_logs before the delete query from Emp_data table is executed to delete a row. The trigger code is written as follows. Now, we will check the trigger by deleting a row from Emp_data table.
Can a table have multiple triggers in MySQL?
MySQL 5.7.2+ lifted this limitation and allowed you to create multiple triggers for a given table that have the same event and action time. These triggers will activate sequentially when an event occurs. Here is the syntax for defining a trigger that will activate before or after an existing trigger in response to the same event and action time:
The administrator can manage the patrons. When they choose to remove a patron, the patron is removed from the table 1 patrons. At this point, nothing happens to table 2 patron_info. I’m simply trying to create a trigger to delete from table 2, when table 1 has an item deleted. Here’s what I’ve tried…