>> Don't know whether windowing functions can be used in the WHERE clause, but when Firebird 3 is released, it would be tempting to try things like
>>
>> WHERE MOD(ROW_NUMBER() OVER (ORDER BY <something>), 5) = 2
>
>You shouldn't be able to use window functions in a `WHERE`, only in the
>`SELECT` columnlist. The `ROW_NUMBER` is applied over the materialized
>rows, so you can't apply it in the filtering condition. You need a
>subquery or CTE with `ROW_NUMBER()` and then filter that in the outer
>select.

Thanks for confirming things to work more like I expected them to, rather than what I hoped. Anyway, adding a CTE is only a minor overhead.

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