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There's no good reason why you couldn't rewrite DISTINCT to GROUP BY, but remember that it wouldn't work in all cases; you could have both. E.g. SELECT DISTINCT

There's no good reason why you couldn't rewrite DISTINCT to GROUP BY, but remember that it wouldn't work in all cases; you could have both. E.g. SELECT DISTINCT COUNT(*) FROM t1 GROUP BY a;. Similarly, HAVING and window functions happen after GROUP BY but before DISTINCT, so a simple move won't always be correct and you'd have to account for that.

_a_a_a_ 3y ago
> There's no good reason why you couldn't rewrite DISTINCT to GROUP BY Exactly. People post a lot of things about SQL optimisation without knowing anything about it. Frankly, I'm getting really fed up with it on HN.