"Jim Starkey" <jas@...> wrote:

>
> Within a context, a field has precedence over an alias. But an alias
> has precedence over a earlier context.

Although I'm still not convienced that we need alias-based references, I'd choose this Jim's rule for possible implementation in the case it would happen. Now let's look at the suggested boundary example:

SELECT F1 AS F2
FROM TAB
WHERE F2 = 0

Usage of the aforementioned rule would mean different results to be returned depending on existence of the column F2 in TAB. Personally, I don't like it. Too many chances for a programmer's mistake. Since I never liked undefined behaviour of any kind either, this means that I'd stick with choice C in Jim's terminology, i.e. throw an ambiguity error.


Dmitry