MySQL: ALTER IGNORE TABLE ADD UNIQUE, what will be truncated?

Question

I have a table with 4 columns: ID, type, owner, description. ID is AUTO_INCREMENT PRIMARY KEY and now I want to:

ALTER IGNORE TABLE `my_table`
    ADD UNIQUE         


        

Answer 1

It appears that your problem is one of the very reasons that ALTER IGNORE has been deprecated.

This is from the MySQL notes on the ALTER IGNORE deprecation:

"This feature is badly defined (what is the first row?), causes problems for replication, disables online alter for unique index creation and has caused problems with foreign keys (rows removed in parent table)."