SELECT n.nspname,
       t.relname as table, 
       c.conname as pk_name
  FROM pg_class t
  JOIN pg_constraint c ON ( c.conrelid = t.OID AND c.contype = 'p')
  JOIN pg_namespace n  ON (n.oid = t.relnamespace)
 WHERE relkind = 'r'
   AND t.relname NOT LIKE 'pg_%'
   AND t.relname NOT LIKE 'sql_%'
   ORDER BY n.nspname, t.relname, c.conname;