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Unnecessary DISTINCT
Applies to ✅ Open Source Edition ✅ Express Edition ✅ Professional Edition ✅ Enterprise Edition
When every GROUP BY expression is also projected in a SELECT DISTINCT clause at least once, in any order, then the DISTINCT keyword is unnecessary.
Using Settings.transformPatternsUnnecessaryDistinct, the following transformations can be achieved:
-- With Settings.transformPatternsUnnecessaryDistinct active, this: SELECT DISTINCT b, a, count(*) FROM t GROUP BY a, b; -- ... is transformed into the equivalent expression: SELECT b, a, count(*) FROM t GROUP BY a, b;
In simpler cases, such as projection only queries, DISTINCT is also never necessary:
-- With Settings.transformPatternsUnnecessaryDistinct active, this: SELECT DISTINCT 1, count(*); -- ... is transformed into the equivalent expression: SELECT 1, count(*);
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