Postgres 10

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CREATE TABLE t AS SELECT generate_series (1, 100000) t_id;

ALTER TABLE t ADD PRIMARY KEY (t_id);

SELECT 100000

ALTER TABLE

EXPLAIN ANALYZE
SELECT t_id FROM t
WHERE  t_id IN (SELECT generate_series(1,103));

QUERY PLAN

Nested Loop  (cost=17.81..1118.27 rows=50000 width=4) (actual time=0.132..0.326 rows=103 loops=1)

  ->  HashAggregate  (cost=17.52..19.52 rows=200 width=4) (actual time=0.034..0.055 rows=103 loops=1)

        Group Key: generate_series(1, 103)

        ->  ProjectSet  (cost=0.00..5.02 rows=1000 width=4) (actual time=0.004..0.013 rows=103 loops=1)

              ->  Result  (cost=0.00..0.01 rows=1 width=0) (actual time=0.001..0.001 rows=1 loops=1)

  ->  Index Only Scan using t_pkey on t  (cost=0.29..6.53 rows=1 width=4) (actual time=0.002..0.002 rows=1 loops=103)

        Index Cond: (t_id = (generate_series(1, 103)))

        Heap Fetches: 103

Planning time: 0.721 ms

Execution time: 7.797 ms

EXPLAIN

EXPLAIN ANALYZE
SELECT t_id FROM t
WHERE  t_id IN  (1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20
                ,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40
                ,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60
                ,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80
                ,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100,101, 102, 103);

QUERY PLAN

Bitmap Heap Scan on t  (cost=378.93..637.38 rows=103 width=4) (actual time=0.268..0.656 rows=103 loops=1)

  Recheck Cond: (t_id = ANY ('{1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100,101,102,103}'::integer[]))

  Heap Blocks: exact=1

  ->  Bitmap Index Scan on t_pkey  (cost=0.00..378.90 rows=103 width=0) (actual time=0.254..0.254 rows=103 loops=1)

        Index Cond: (t_id = ANY ('{1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100,101,102,103}'::integer[]))

Planning time: 0.150 ms

Execution time: 2.774 ms

EXPLAIN