Re: Query Plan

Theo Galanakis wrote:
> 
> Have a question regarding when a Query Plan uses an Index.
> 
> I have a basic statement
> 
> This query uses the Index Scan:
> explain analyse select * from tablea where columna_id < 57
> 
> This query uses Seq Scan:
> explain analyse select * from tablea where columna_id < 58
> 
> There are about 5000 records in this table, and columna_id is the primary
> key, which is Indexed... And recently recreated.

OK - what does explain analyse say?

Each line will have two parts, the expected costs/number of rows and the 
actual time/number of rows.

If PG is expecting say 50 rows in the first query but 150 in the second 
then it might decide a sequential scan is quicker.

Post the outputs of explain analyse and we can compare them.
--   Richard Huxton  Archonet Ltd