Tom Lane wrote:
"Joshua D. Drake" <[EMAIL PROTECTED]> writes:
Tom Lane wrote:
"Joshua D. Drake" <[EMAIL PROTECTED]> 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



--

      === The PostgreSQL Company: Command Prompt, Inc. ===
Sales/Support: +1.503.667.4564 || 24x7/Emergency: +1.800.492.2240
Providing the most comprehensive  PostgreSQL solutions since 1997
             http://www.commandprompt.com/

Donate to the PostgreSQL Project: http://www.postgresql.org/about/donate
PostgreSQL Replication: http://www.commandprompt.com/products/


---------------------------(end of broadcast)---------------------------
TIP 3: Have you checked our extensive FAQ?

              http://www.postgresql.org/docs/faq

Reply via email to