"1292 Incorrect datetime value" when updating an "empty" datetime field
Congratulation on your commitment to clean dates.
Temporary disabling the NO_ZERO_DATE sql_mode will enable this cleanup.
Just to be sure, use 0000-00-00 00:00:00 as the date too.
SET @@SQL_MODE = REPLACE(@@SQL_MODE, 'NO_ZERO_DATE', '');
UPDATE mytable
SET updated_at=created_at
WHERE (updated_at='' OR updated_at='0000-00-00 00:00:00') and id &gt;0;