Populate the usr table for existing Tempo news entry authors. insert into usr (username) (select distinct fe.author from tp_feed_entry fe where not exists (select u.username from usr u where u.username = fe.author)) Populate the usr table for existing Tempo news entry authors. insert into usr (id, username) select usr_sq.nextval, tmp.author from ( select distinct fe.author from tp_feed_entry fe where not exists (select u.username from usr u where u.username = fe.author)) tmp Create a new column author_id in tp_feed_entry Migrate data from author to author_id update tp_feed_entry set author_id = ( select usr.id from usr where usr.username = tp_feed_entry.author ); Set author_id column to be non-nullable Drop the old author column