v.21.9Improvement

Merge JOIN Handles Empty Right Set Correctly

Official CH changelog text
Merge JOIN correctly handles empty set in the right. #27078 (Vladimir C).
Merge JOIN now correctly handles cases where the right side of the join is an empty set.

Why it matters

This feature fixes the behavior of Merge JOIN when the right input dataset is empty. Previously, such cases might have been handled incorrectly, leading to unexpected results. Ensuring correct handling improves the reliability and correctness of join operations in queries involving empty datasets.

How to use it

This fix is applied implicitly to Merge JOIN operations, so users do not need to enable or configure anything separately. Simply perform JOIN queries as usual, and cases with empty right-side inputs will be handled correctly.

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