This is experimental functionality, and as such subject to change. Use at your own risk!
Unnecessary EXISTS subquery clauses
Applies to ✅ Open Source Edition ✅ Express Edition ✅ Professional Edition ✅ Enterprise Edition
The EXISTS predicate can safely ignore a few of its subquery clauses without changing semantics, including:
- The SELECT clause
- The DISTINCT clause
- The ORDER BY clause
- The LIMIT clause, if it is non-zero
All of the above applies only if there are no aggregate functions in the EXISTS subquery.
Using Settings.transformPatternsUnnecessaryExistsSubqueryClauses, the following transformations can be achieved:
-- With Settings.transformPatternsUnnecessaryExistsSubqueryClauses active, this: SELECT EXISTS (SELECT DISTINCT a, b FROM t); -- ... is transformed into the equivalent expression: SELECT EXISTS (SELECT 1 FROM t);
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