Fix exception in concat with Variant containing LowCardinality#97654
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alexey-milovidov merged 4 commits intomasterfrom Feb 23, 2026
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Fix exception in concat with Variant containing LowCardinality#97654alexey-milovidov merged 4 commits intomasterfrom
alexey-milovidov merged 4 commits intomasterfrom
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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>
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Cherry pick #97654 to 25.3: Fix exception in concat with Variant containing LowCardinality
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Cherry pick #97654 to 25.8: Fix exception in concat with Variant containing LowCardinality
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Cherry pick #97654 to 25.11: Fix exception in concat with Variant containing LowCardinality
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Cherry pick #97654 to 25.12: Fix exception in concat with Variant containing LowCardinality
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Cherry pick #97654 to 26.1: Fix exception in concat with Variant containing LowCardinality
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Backport #97654 to 26.1: Fix exception in concat with Variant containing LowCardinality
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…ntaining `LowCardinality` Same bug as fixed for `concat` in ClickHouse#97654: `convertToFullIfNeeded` recursively strips `LowCardinality` from inside compound column types like `Variant`, but 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`. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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…t-low-cardinality Fix exception in concat with Variant containing LowCardinality
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Summary
Bad cast from type DB::ColumnVector<char8_t> to DB::ColumnLowCardinality) in theconcatfunction when an argument is an array containing aVarianttype withLowCardinalityinside (e.g.,concat('a', [(1, 2), toLowCardinality(3)]))convertToFullIfNeededrecursive — it now stripsLowCardinalityfrom inside compound column types likeColumnVariant, but the argument type is not updated to match, causing a type/column mismatch during serializationconvertToFullIfNeededCI report: https://s3.amazonaws.com/clickhouse-test-reports/json.html?PR=97581&sha=320e7c9d8876b04a971bd26214b9ac0ab433c250&name_0=PR&name_1=AST%20fuzzer%20%28amd_debug%29
Test plan
03987_concat_variant_low_cardinalitywith reproducer queriesconcatfunctionality is not affectedChangelog category (leave one):
Changelog entry (a user-readable short description of the changes that goes into CHANGELOG.md):
Fix LOGICAL_ERROR exception in
concatwhen an argument contains aVarianttype withLowCardinalityinside.🤖 Generated with Claude Code