Martijn van Oosterhout <kleptog@xxxxxxxxx> writes:
> Something twigged telling me that in fact the latter expression is not
> in standard SQL but a (very common) extension. A <sort key> is clearly
> indicated to be a <value expression> with no indication anywhere that
> column aliases are allowed here (though that may be in the common rules
> somewhere).
SQL92 says differently. The committee basically redefined ORDER BY
entirely between SQL92 and SQL99.
What we actually try to support is both SQL92 and SQL99 interpretations,
which is a pretty unholy mess, but enough people (and programs) are used
to the SQL92 way that I don't foresee being able to drop it.
regards, tom lane
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