Thread: identify Tables without primary keys - postgres

Dear all -

             I have the following query to find the tables with primary keys. can you please help me finding the tables without primary key.

             select
 distinct x.table_name,
from
 information_schema.constraint_column_usage x,
 pg_constraint b
where
 b.contype='p' and
 x.constraint_name=b.conname

Regards