Simplify UNION ALL with identical expressions but different aliases#69
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kyleconroy merged 2 commits intomainfrom Dec 28, 2025
Merged
Simplify UNION ALL with identical expressions but different aliases#69kyleconroy merged 2 commits intomainfrom
kyleconroy merged 2 commits intomainfrom
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ClickHouse's EXPLAIN AST output optimizes UNION ALL queries when all SELECTs have identical expressions but different column aliases. Since column names come from the first SELECT, subsequent SELECTs are elided in the AST output. This adds simplifyUnionSelects() to match this behavior, fixing test 00592_union_all_different_aliases.
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ClickHouse's EXPLAIN AST output optimizes UNION ALL queries when all
SELECTs have identical expressions but different column aliases. Since
column names come from the first SELECT, subsequent SELECTs are elided
in the AST output.
This adds simplifyUnionSelects() to match this behavior, fixing test
00592_union_all_different_aliases.