08.10.2009, в 17:30, kokok_kokok написал(а):

> In few words, index is absolutely necessary.
>

In my application I need index on calculated column.
As FB doesn't allow index on such columns, I use following trick:

- add normal column
- calculate this column as needed in triggers
- index works on this column

May be this approach is applicable in your case too?
It must be so if it possible to build two functions:
1) from A to desc A
2) from desc A to A

Regards

Valeri