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Fix logical error in correlated subqueries with group_by_use_nulls#108714
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Fix logical error in correlated subqueries with group_by_use_nulls#108714coderashed wants to merge 2 commits into
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A correlated scalar subquery referencing an outer `GROUP BY` key that becomes `Nullable` via `group_by_use_nulls` (`GROUPING SETS` / `ROLLUP` / `CUBE` / `WITH TOTALS`) aborted with: Logical error: Unexpected return type from toString. Expected String. Got Nullable(String) The `group_by_use_nulls` nullability walk in `resolveExpressionNode` stops at the subquery's own query scope, so a correlated column kept its non-`Nullable` type while decorrelation fed in the real `Nullable` column, mismatching a baked function result type (`toString` -> `String` vs `Nullable(String)`). Continue the walk past a subquery's query boundary for correlated columns and convert the column to `Nullable` in place, preserving the node identity shared with the subquery's correlated-columns set (which the planner matches by identity). Discovered by the AST fuzzer in the `amd_msan` stress test: https://github.com/ClickHouse/ClickHouse/actions/runs/28286443407/job/83839128485?pr=108685 Related: ClickHouse#108685
Add the query shape the AST fuzzer aborted on in the `amd_msan` stress test of ClickHouse#108685 (multi-column projection with a correlated scalar subquery over a `GROUPING SETS` key under `WITH TOTALS`), scaled down and deterministic, so the regression test ties directly to the reported failure.
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Two test cases contributed by @coderashed (who closed his duplicate PR ClickHouse#108714 in favour of this one): 1. The exact AST-fuzzer seed query from ClickHouse#108714: a correlated scalar subquery toString(number) inside concat() over a GROUPING SETS key. Aborts on master with 'Bad cast ColumnNullable to ColumnString', returns s0..s4 with the fix. 2. A type-pinning EXPLAIN QUERY TREE check. The existing cases assert query results, which still pass if a future change silently stops wrapping the correlated key as Nullable (values unchanged, declared type wrong). These pin the analyzer-assigned types via SELECT ... FROM (EXPLAIN QUERY TREE ...) WHERE explain ILIKE '%...%', so dropping the Nullable wrapping fails with a clean diff. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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Closes: #107445
Closes: #106377
Related: #107951
Related: #108685
Related: #104350
Fixes a logical error in correlated scalar subqueries when an outer
GROUP BYkey is madeNullablebygroup_by_use_nulls(throughGROUPING SETS/ROLLUP/CUBE/WITH TOTALS).A correlated column referencing such an outer key was left non-
Nullableby the analyzer: thegroup_by_use_nullsnullability walk inresolveExpressionNodestops at the subquery's own query scope and never reaches the outer scope that owns the key. At decorrelation time the plan feeds in the realNullablecolumn, so a baked function result type (e.g.toString->String) no longer matches the actualNullable(String), aborting with:The fix lets the scope walk continue past a subquery's query boundary for correlated columns and converts the correlated column to
Nullablein place, preserving the node identity shared with the subquery's correlated-columns set (which the planner matches by identity).How it was found
Discovered by the AST fuzzer in the
amd_msanstress test of #108685: https://github.com/ClickHouse/ClickHouse/actions/runs/28286443407/job/83839128485?pr=108685The exact query the fuzzer aborted on (seeded from
02122_parallel_formatting_CSV):Minimal reproducer:
Testing
04413_correlated_subquery_group_by_use_nullscoversGROUPING SETS/ROLLUP/CUBE/WITH TOTALS, asserts the correlated result isNullable, checks a non-correlated subquery is unaffected, and includes the exact (scaled-down) query shape from the CI failure above.*correlated*,*group_by_use_nulls*and*grouping_sets*stateless tests pass locally with the fix.Changelog category (leave one):
Changelog entry (a user-readable short description of the changes that goes into CHANGELOG.md):
Fix a logical error (
Unexpected return type ...) when a correlated scalar subquery references an outerGROUP BYkey that becomesNullabledue togroup_by_use_nulls(GROUPING SETS/ROLLUP/CUBE/WITH TOTALS).