Coming from a Rails background, I have a large production database that I have a copy of where I only need records from 4 of the 2000+ companies. I'm trying to delete all the rows except the ones belonging to the 4, and I know the way I have it is not optimal.
DELETE FROM appointments WHERE (appointments.company_id NOT IN (6, 753, 785, 1611))
another example is when I have to delete records on a table where the company_id is on an associated table:
DELETE FROM mappings WHERE mappings.id IN (SELECT mappings.id FROM code_mappings INNER JOIN codes ON codes.remote_id = mappings.code_remote_id WHERE (codes.company_id NOT IN (6, 753, 785, 1611)))