For hazards without authors, make Administrator the author update tp_comment set author = 'Administrator' where author is null Populate the usr table for existing comment authors. insert into usr (username) (select distinct cm.author from tp_comment cm where not exists (select u.username from usr u where u.username = cm.author)) Populate the usr table for existing comment authors. insert into usr (id, username) select usr_sq.nextval, tmp.author from ( select distinct cm.author from tp_comment cm where not exists (select u.username from usr u where u.username = cm.author)) tmp Create a new column for author_id in tp_comment Migrate data from author to author_id update tp_comment set author_id = ( select usr.id from usr where usr.username = tp_comment.author ); Set author_id column to be non-nullable Drop the old author column