Re: Query composite index range in an efficient way

On Tue, 17 Feb 2009, Havasvölgyi Ottó wrote:
> I created a big enough table (131072 records, and it had also a 3rd
> field with about 120 character text data). But Postgres performs a
> SeqScan.

Firstly, you should always post EXPLAIN ANALYSE results when asking about
a planning problem.

Secondly, you can't "get" Postgres to choose a particular plan (without
disruptive fiddling with the planner). Postgres will try to choose the
plan that answers the query fastest, and this may be a sequential scan.

What happens if you use the following WHERE clause?

WHERE id1 > 12 AND id1 < 56

Does Postgres use a sequential scan then?

How many rows does your query return? If it's more than about 10% of the
total rows in the table, then a sequential scan is probably the fastest
method.

Matthew

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