ctid explain

gistfile1.txt

                                            QUERY PLAN
--------------------------------------------------------------------------------------------------
 Merge Join  (cost=186.30..212.30 rows=500 width=6)
   Merge Cond: (film.ctid = (((('(0,'::text || (s.i)::text) || ')'::text))::tid))
   ->  Sort  (cost=113.83..116.33 rows=1000 width=6)
         Sort Key: film.ctid
         ->  Seq Scan on film  (cost=0.00..64.00 rows=1000 width=6)
   ->  Sort  (cost=72.48..72.98 rows=200 width=4)
         Sort Key: (((('(0,'::text || (s.i)::text) || ')'::text))::tid)
         ->  Unique  (cost=59.83..64.83 rows=200 width=4)
               ->  Sort  (cost=59.83..62.33 rows=1000 width=4)
                     Sort Key: (((('(0,'::text || (s.i)::text) || ')'::text))::tid)
                     ->  Function Scan on generate_series s  (cost=0.00..10.00 rows=1000 width=4)
(11 rows)