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