On 13/09/10 19:48, Tom Lane wrote:
Gaetano Mendola<mendola@xxxxxxxxx> writes:
Of course I'm not suggesting to take away the "sort by" and give the user
an unsorted result, I'm asking why the the optimizer in cases like:
select unique(a) from v_table_with_order_by;
doesn't takes away the "order by" inside the view and puts it back "rewriting the
query like this:
select unique(a) from v_table_without_order_by
order by a;
That changes the order in which the rows are fed to unique(a). The
principal real-world use for a non-top-level ORDER BY is exactly to
determine the order in which rows are fed to a function, so we will
have a revolt on our hands if we break that.
You could check for volatile functions. I think this could be done
safely. However, it doesn't seem worthwhile, it would be a fair amount
of code, and it's not usually a good idea to put an ORDER BY in a view
or subquery anyway unless you also have volatile functions in there, or
you want to coerce the optimizer to choose a certain plan.
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com
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