On Jan 8, 2007, at 01:24, Svein Erling Tysvaer wrote:

> Do you use this in your WHERE clause and use the new Fb 2
> functionality
> of expression indexes? To me, it seems more like some statement to use
> in the SELECT part (which doesn't use indexes anyway). And if you
> really
> use it in the where clause and have indexed func(arg), I would expect
> that changing

We allow users to define derived columns, which can be used both for
filtering (when indexing and even joins come into play) or for
aggregation (SUM(func(arg)). And such functions can be endlessly
stacked. So we would have to generate the indexes on the fly, and
they would only be useful in certain situations.

> WHERE (CASE WHEN arg is NULL THEN CAST(NULL AS result_type) ELSE
> func(arg)
> END) = <value or other expression>
>
> into
>
> WHERE (CASE WHEN arg is NULL THEN CAST(NULL AS result_type) ELSE
> func(arg)
> END) = <value or other expression> AND
> func(arg) = <value or other expression>
>
> would produce the same result and use the expression index (though I
> would of course expect NULL to not equal any record since NULL isn't
> even equal to NULL).

That is where Firebird's very nice "IS NOT DISTINCT FROM" operator
comes in handy.
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Richard Wesley Senior Software Developer Tableau
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