This is perhaps a more elegant alternative solution to that in #382 / #383.

MySQL does not provide a duplicate-specific ignore. But it does have ON DUPLICATE KEY UPDATE. It can be co-opted to play the role of the ON DUPLICATE KEY IGNORE.

I propose to replace the logic implemented in #383 by appending ON DUPLICATE KEY UPDATE id1 = id1 where id1 is the first attribute of the primary key. This leaves the duplicate values unchanged and quietly ignores them while inserting all the good entries.