Re: Constraint exclusion oddity with composite index - Mailing list pgsql-hackers

"Joshua D. Drake" <jd@commandprompt.com> writes:
> Tom Lane wrote:
>> "Joshua D. Drake" <jd@commandprompt.com> writes:
>>> Assume the following:
>>> index on: (id, adate)
>>> constraint CHECK(adate > '01-01-2007' AND adate < '04-01-2007');
>>> The planner will not use the index listed above.
>> 
>> For what?

> select adate from parent where adate = '01-25-2007'

That's unsurprising.  Searching with only a lower-order index column
value seldom wins, 'cause you've got to scan the entire index.  The
constraint is irrelevant to this.
        regards, tom lane