Re: Timestamp indexes

"Mitch Vincent" <mitch@venux.net> writes:
> A while back I as told (by Tom Lane I *think*) that timestamp (previously
> datetime) fields couldn't be indexed as such

That's certainly not true now, if it ever was...

regression=# create table applicants(resubmitted timestamp);
CREATE
regression=# create index applicants_i on applicants(resubmitted);
CREATE
regression=# explain select * from applicants where resubmitted = 'today';
NOTICE:  QUERY PLAN:

Index Scan using applicants_i on applicants  (cost=0.00..8.14 rows=10 width=8)

EXPLAIN

> and that I should index them
> using this method :

> CREATE  INDEX "applicants_resubmitted" on "applicants" using btree ( date
> ("resubmitted") "date_ops" );

> Since almost all the queries that search that field  search it casting the
> field to date, I thought that would be OK.. It was for a while (in the 6.5.X
> days) but it seems that 7.0.2 is treating this different. I can't get an
> index scan on that field no matter what I do.

Dunno, it works for me ...

regression=# CREATE  INDEX "applicants_resubmitted" on "applicants"
regression-# (date("resubmitted") "date_ops" );
CREATE
regression=# explain select * from applicants where date(resubmitted) = 'today';
NOTICE:  QUERY PLAN:

Index Scan using applicants_resubmitted on applicants  (cost=0.00..8.16 rows=10
width=8)

EXPLAIN
regression=# explain select * from applicants where resubmitted::date = 'today';
NOTICE:  QUERY PLAN:

Index Scan using applicants_resubmitted on applicants  (cost=0.00..8.16 rows=10
width=8)

EXPLAIN

You would want an index on date() of the field if this is what most of
your queries look like --- a straight index on the timestamp isn't
useful for such a query.  But I don't know why you're not getting
index scans.  More details please?
        regards, tom lane