Re: Where clause efficiency using "IN"

* Sean Davis <sdavis2(at)mail(dot)nih(dot)gov> [2004-10-22 11:07:45 -0400]:

> Just a quick general question: Can someone comment on using where
> clauses like:
>
> (sample = 2 OR sample = 3 OR sample = 4)
>
> as compared to
>
> sample in (2,3,4)
>
> in terms of efficiency?

The 'explain analyze' command is helpful for making these kinds of decisions. In 7.4.5 it's translated to an OR.

xinu=# explain analyze select id from users where id in (14, 30);
QUERY PLAN
---------------------------------------------------------------------------------------------------------------
Seq Scan on users (cost=100000000.00..100000012.50 rows=2 width=8) (actual time=0.045..0.050 rows=2 loops=1)
Filter: ((id = 14) OR (id = 30))
Total runtime: 0.079 ms
(3 rows)

xinu=# explain analyze select id from users where id = 14 or id = 30;
QUERY PLAN
---------------------------------------------------------------------------------------------------------------
Seq Scan on users (cost=100000000.00..100000012.50 rows=2 width=8) (actual time=0.044..0.049 rows=2 loops=1)
Filter: ((id = 14) OR (id = 30))
Total runtime: 0.077 ms
(3 rows)

HTH,

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