Specifically, I'm imagining that we could convert
SELECT min(x), max(y) FROM tab WHERE ...
into sub-selects in a one-row outer query:
SELECT (SELECT x FROM tab WHERE ... ORDER BY x LIMIT 1), (SELECT y FROM tab WHERE ... ORDER BY y DESC LIMIT 1);
Does this transformation work for a query of the form:
SELECT min(x), max(y) FROM tab WHERE random() > 0.5;
(which isn't a very useful query, but I'm sure you can imagine a more realistic example involving volatile functions in the WHERE clause.)
-Neil
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