Обсуждение: Use of Indexes

Hello,

I am trying out a few databases to determine which one would best suit a
project.

I was wondering if someone could answer a question about how PostgreSQL uses
indexes when performing queries. Particularly, I need to know if the query
optimizer will use more than index for a query or if it only uses one.

For instance, one of my tables (1 million records) contains a document
number, a document type, a received date, a review date, an entered date,
and an audited date.

If I want to retrieve the following pieces of data:

all of the documents of type 1 that were received yesterday
all of the documents of type 2 that were entered yesterday
all of the documents of type 2 that were reviewed yesterday

Would I be able to create individual indexes on type, received date, entered
date, and reviewed date and the optimizer would select the appropriate two
indexes, or would I have to create three composite indexes that would
include type-received, type-entered, and type-reviewed?

Thanks for the help.

Darrell

"Darrell A. Sullivan, II" <darrell@flores-associates.com> writes:
> I was wondering if someone could answer a question about how PostgreSQL uses
> indexes when performing queries. Particularly, I need to know if the query
> optimizer will use more than index for a query or if it only uses one.

Versions through 8.0 can only use one index per query (per table).  8.1
will be smarter though.

            regards, tom lane