Re: using CURSOR with PHP

On Sun, 2002-05-19 at 06:32, Keary Suska wrote:
>
> The drawback to using LIMIT is that you are executing the query on every
> call, and Postgres cannot optimize on a LIMIT as was mentioned, because the
> entire query has to be collected before the LIMIT can be applied. However,
> IIRC, Postgres does query result caching, so subsequent calls on the same
> query will tend to be faster, providing there is enough memory allocated to
> support it.

PostgreSQL will certainly take LIMIT into account when planning queries.

EXPLAIN SELECT * FROM mybigtable WHERE x = y;

and

EXPLAIN SELECT * FROM mybigtable WHERE x = y LIMIT n;

Will regularly show different query plans.

For more complex queries, however, the plans are less likely to differ
by much.

OTOH PostgreSQL does _not_ do result caching, unless you have applied
some patches that were floating around last year some time.

Regards,
Andrew.
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