Re: Increase performance of a UNION query that thakes - Mailing list pgsql-performance

On Fri, 6 Feb 2004, Bruno BAGUETTE wrote:

> I was thinking that a index on lower(substr(l_name, 1, 1)) and another
> index on lower(substr(org_name, 1, 1)) should gives better performances.
> When I've to create theses two indexes, it seems like this is not
> allowed :
>
> levure=> CREATE INDEX firstchar_lastname_idx ON
> people(lower(substr(l_name, 1, 1)));
> ERROR:  parser: parse error at or near "(" at character 59

In 7.4, I believe you would say
 on people((lower(substr(l_name,1,1))))
but I'm not sure that index would really help in practice.

> Do you have another idea to get better performances ?

In addition to what Tom said, the row estimates look suspiciously default.
You mention vacuuming, but do you ever analyze the tables?

Also, what do you have sort_mem set to?