On 9-10-2018 16:46, Hugo Eyng hugoeyng@... [firebird-support] wrote:

> I created an index on a table where de column is datetime type. The
> problem seems to be related to the NULL value.
>
> This SQL is very *_SLOW_* (about 7 seconds for a table containing
> 360.000 records). Returns around 400 records
> SELECT
> A.cd_xxx, A.dt_1, A.dt_2, A.dt_3, A.dt_4, A.dt_5, A.dt_index​
> FROM DM251 A​
> WHERE    A.DT_INDEX*_IS_* NULL
>
> This SQL is very *_FAST_* (less than 0.5 seconds for a table containing
> 360.000 records). Returns around 359.600 records
>
> SELECT
> A.cd_xxx, A.dt_1, A.dt_2, A.dt_3, A.dt_4, A.dt_5, A.dt_index​
> FROM DM251 A​
> WHERE    A.DT_INDEX*_IS NOT_* NULL

What version Firebird are you using (full version please), and what is
the column type?

Mark
--
Mark Rotteveel