[firebird-support] Very slow select Index with null date

[Hugo Eyng hugoe...@msn.com [firebird-support]]

Hello.

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



Atenciosamente,

+ + Hugo Eyng + +