Re: pattern matching with dates?

On 07/01/11 14:15, pasman pasmański wrote:
> Sorry, but this examples not use index.

Looks like it does here (oh, and please try to post your replies at the
bottom of the message)

> On 1/7/11, Susanne Ebrecht<susanne(at)2ndquadrant(dot)com> wrote:

>> The more proper way is:
>> SELECT * from tab WHERE EXTRACT(YEAR FROM log_date) = 2011 and
>> EXTRACT(MONTH FROM log_date) = 1;

CREATE TABLE d_table (d date);
INSERT INTO d_table SELECT '2001-01-01'::date + generate_series(1,9999);
CREATE INDEX d_extract_idx ON d_table ( extract('day' FROM d) );
EXPLAIN ANALYSE SELECT * FROM d_table WHERE extract('day' FROM d) = 3;

That ends up doing a bitmap index scan for me.

Of course, it's entirely possible an index on year+month returns too
many rows to be useful.

--
Richard Huxton
Archonet Ltd