Re: IN(subselect returning few values ...)

Stephen Frost <sfrost(at)snowman(dot)net> writes:
> Working on 8.1 I've recently been annoyed at the need to translate a
> sub-select inside an IN () clause into a fixed list of contents (the
> results of the sub-select, exactly) in order to get better performance.

Better performance than what? Ever since 7.4 we've converted small IN
sub-selects into plans along the lines of

regression=# explain select * from tenk1 where unique1 in (select f1 from int4_tbl);
QUERY PLAN
-----------------------------------------------------------------------------------
Nested Loop (cost=1.06..31.20 rows=5 width=244)
-> HashAggregate (cost=1.06..1.11 rows=5 width=4)
-> Seq Scan on int4_tbl (cost=0.00..1.05 rows=5 width=4)
-> Index Scan using tenk1_unique1 on tenk1 (cost=0.00..6.00 rows=1 width=244)
Index Cond: (tenk1.unique1 = "outer".f1)
(5 rows)

which looks OK to me.

regards, tom lane