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Unreachable CASE clauses
Applies to ✅ Open Source Edition ✅ Express Edition ✅ Professional Edition ✅ Enterprise Edition
When a searched CASE expression contains unreachable WHEN or ELSE clauses, we can remove them.
Using Settings.transformPatternsUnreachableCaseClauses, the following transformations can be achieved:
-- With Settings.transformPatternsUnreachableCaseClauses active, this: SELECT CASE WHEN a = b THEN 1 WHEN TRUE THEN 2 WHEN c = d THEN 3 END, CASE WHEN a = b THEN 1 WHEN FALSE THEN 2 WHEN c = d THEN 3 END FROM tab; -- ... is transformed into the equivalent expression: SELECT CASE WHEN a = b THEN 1 ELSE 2 END, CASE WHEN a = b THEN 1 WHEN c = d THEN 3 END FROM tab;
A more subtle unreachable WHEN clause is a clause that has already been listed, irrespective of the THEN clause. While removing it is a correct transformation, the duplicate might be likely due to a typo.
-- With Settings.transformPatternsUnreachableCaseClauses active, this:
SELECT
CASE
WHEN a = b THEN 1
WHEN c = d THEN 2
WHEN a = b THEN 3
END
FROM tab;
-- ... is transformed into the equivalent expression:
SELECT
CASE
WHEN a = b THEN 1
WHEN c = d THEN 2
END
FROM tab;
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