Tom Lane wrote:
> "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.
I guess where I got confused is:
http://www.postgresql.org/docs/8.1/static/indexes-multicolumn.html
And explicitly:
A multicolumn B-tree index can be used with query conditions that
involve any subset of the index's columns, but the index is most
efficient when there are constraints on the leading (leftmost) columns.
Sincerely,
Joshua D. Drake
>
> regards, tom lane
>
> ---------------------------(end of broadcast)---------------------------
> TIP 2: Don't 'kill -9' the postmaster
>
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