Cherry pick #97654 to 25.8: Fix exception in concat with Variant containing LowCardinality#97784
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robot-ch-test-poll2 merged 5 commits intobackport/25.8/97654from Feb 23, 2026
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The `concat` function's `executeFormatImpl` called `convertToFullIfNeeded` which, after it was made recursive in #97493, strips `LowCardinality` from inside compound column types like `Variant`. However, the argument type is not updated to match, so `SerializationLowCardinality` tries to cast a non-LC column, triggering a LOGICAL_ERROR exception in debug builds. Fix by using only top-level column conversions (Const, Sparse, LowCardinality) instead of the recursive `convertToFullIfNeeded`, keeping the column structure consistent with the type's serialization. https://s3.amazonaws.com/clickhouse-test-reports/json.html?PR=97581&sha=320e7c9d8876b04a971bd26214b9ac0ab433c250&name_0=PR&name_1=AST%20fuzzer%20%28amd_debug%29 Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
…inality Fix exception in concat with Variant containing LowCardinality
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Original pull-request #97654
Do not merge this PR manually
This pull-request is a first step of an automated backporting.
It contains changes similar to calling
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