Originally Posted by ry0t

The purpose of the IGNORE keyword (e.g. INSERT IGNORE) is
to allow one to INSERT/UPDATE large numbers of rows,
ignoring any that contain invalid data. The idea is that it will
normally be used when recopying already verified data, and
that any invalid data found will be further investigated by the
user -- and that all the valid data will be accepted, regardless
of the invalid data errors found.