v.25.12Backward Incompatible Change

Is now forbidden to create special MergeTree

Official CH changelog text
It is now forbidden to create special MergeTree tables (such as ReplacingMergeTree, CollapsingMergeTree, etc.) with an empty ORDER BY key, since merge behavior in these tables is undefined. If you still need to create such a table, enable the allow_suspicious_primary_key setting. #91569 (Anton Popov).
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