Re: explain analyze rows=%.0f

Hi! I got a query plan with a strange number of rows. Could you please
help me understand it?

create temp table ta (id int primary key, val int);
create temp table tb (id int primary key, aval int);
create temp table tc (id int primary key, aid int);
insert into ta select id, id from generate_series(1,1000) as id;
insert into tb select id, id from generate_series(500,1000) as id;
insert into tc select id, id from generate_series(400,1000) as id;

EXPLAIN (ANALYZE, COSTS OFF, SUMMARY OFF, TIMING OFF, BUFFERS OFF)
 SELECT 1
   FROM ta ta1
  WHERE EXISTS (SELECT 1
                  FROM tb
                  JOIN tc
                    ON tb.id = ta1.id and
                       ta1.id < 1000
                    where exists (select 1 from ta ta2 where ta2.id =
ta1.id));

                                      QUERY PLAN
--------------------------------------------------------------------------------------
 Seq Scan on ta ta1 (actual rows=500.00 loops=1)
   Filter: EXISTS(SubPlan 2)
   Rows Removed by Filter: 500
   SubPlan 2
     ->  Result (actual rows=0.50 loops=1000)
           One-Time Filter: ((ta1.id < 1000) AND (InitPlan 1).col1)
           InitPlan 1
             ->  Index Only Scan using ta_pkey on ta ta2 (actual
rows=1.00 loops=999)
                   Index Cond: (id = ta1.id)
                   Heap Fetches: 999
           ->  Nested Loop (actual rows=0.50 loops=999)
                 ->  Seq Scan on tb (actual rows=0.50 loops=999)
                       Filter: (id = ta1.id)
                       Rows Removed by Filter: 375
                 ->  Seq Scan on tc (actual rows=1.00 loops=500)
(15 rows)

To be honest I can't understand why 0.50 number of rows here?

--
Regards,
Alena Rybakina
Postgres Professional