branch-4.0: [fix](fe) Fix isCountStar incorrectly treating count(null) as count(*) #62548#62666
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yiguolei merged 1 commit intobranch-4.0from Apr 22, 2026
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#62548) ### What problem does this PR solve? Problem Summary: `Count.isCountStar()` returns `true` for `count(null)` because it only checks `child(0) instanceof Literal` without excluding `NullLiteral`. Since `count(null)` always returns 0 (it counts non-null values of a constant null), it is semantically different from `count(*)` which counts all rows. This could cause incorrect results if downstream rewrite rules (e.g. `PushDownAggThroughJoin`, `SimplifyWindowExpression`, `PushCountIntoUnionAll`) use `isCountStar()` before `CountLiteralRewrite` has a chance to rewrite `count(null)` to `0`. ### Release note Fixed `count(null)` being incorrectly treated as `count(*)` in query optimizer, which could lead to wrong results in certain rewrite scenarios. --------- Co-authored-by: Copilot <[email protected]>
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Cherry-picked from #62548