On 2/2/2013 6:46 PM, Gabor Grothendieck wrote:
In 3.7.11 there was a change to support the feature in the subject
which refers to guaranteeing that y comes from the same row having
maximum x.. See:
http://pages.citebite.com/o9y9n0p9neyt
Did this or other change also enhance the having clause to add a
feature to support a query containing "having max(...)" such as the
query here:
http://r.789695.n4.nabble.com/Filter-according-to-the-latest-data-tp4657248p4657305.html
The query in that thread is of the form "select * from MyTable group by
Name having max(Timestamp)", and the expectation, somehow, is that the
HAVING clause would cause each group to be represented by a row for
which max(Timestamp) is reached. I'm not sure where this expectation
comes from. This is a valid SQL statement whose HAVING clause means
"only include a group in the resultset if max(Timestamp) for this group
is logically true" (that is, not NULL, 0, empty string or empty blob).
A semantic change of the nature you envision is not backward compatible
- it modifies the meaning of existing valid statements. Also, I'm pretty
sure it's not supported by any SQL standard; and I'm not aware of any
DBMS that would interpret the statement the way you want (which doesn't
mean none such exists, of course).
All in all, It seems unlikely that such a proposal would be entertained.
--
Igor Tandetnik
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