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