The release notes for Firebird 2.0 have this example:

CREATE INDEX IDX2 ON T2
COMPUTED BY ( EXTRACT(YEAR FROM COL2) || EXTRACT(MONTH FROM COL2) )

Hence, I'd expect the query you're looking for to be:

CREATE UNIQUE INDEX IDX2 ON T2
COMPUTED BY ( EXTRACT(MONTH FROM COL2) || EXTRACT(YEAR FROM COL2) )

Did you try exactly like this? Maybe you forgot the outer parenthesis?

HTH,
Set

Cipto wrote:

> Hi,
>
> I want to make an unique index base on the expression:
> extract(month from "blnThn")||extract(year from "blnThn")
>
> But it cannot. In what version it will be supported by Firebird?
>
> I use Firebird 2.0 and ODS 11 database
>
>
> TIA