On 05.04.2011 13:19, Marti Raudsepp wrote:
On Fri, Apr 1, 2011 at 14:24, Heikki Linnakangas
<heikki.linnakan...@enterprisedb.com> wrote:
We sometimes transform IN-clauses to a list of ORs:
postgres=# explain SELECT * FROM foo WHERE a IN (b, c);
QUERY PLAN
Seq Scan on foo (cost=0.00..39.10 rows=19 width=12)
Filter: ((a = b) OR (a = c))
But what if you replace "a" with a volatile function? It doesn't seem legal
to do that transformation in that case, but we do it:
postgres=# explain SELECT * FROM foo WHERE (random()*2)::integer IN (b, c);
QUERY PLAN
Seq Scan on foo (cost=0.00..68.20 rows=19 width=12)
Filter: ((((random() * 2::double precision))::integer = b) OR (((random()
* 2::double precision))::integer = c))
Is there a similar problem with the BETWEEN clause transformation into
AND expressions?
marti=> explain verbose select random() between 0.25 and 0.75;
Result (cost=0.00..0.02 rows=1 width=0)
Output: ((random()>= 0.25::double precision) AND (random()<=
0.75::double precision))
Yes, good point.
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com
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