[SPARK-48091][SQL] Preserve aliases inside lambda when ExtractGenerator restructures plan#55892
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…or restructures plan
ExtractGenerator called trimNonTopLevelAliases on all project list items before extracting the generator. This stripped aliases inside lambda functions (e.g., struct(x.as("data"))) before they could be resolved into struct field names by CreateStruct.
Now only uses trimNonTopLevelAliases for pattern matching to detect generators, but preserves the original untrimmed expression for non-generator project items.
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@cloud-fan / @dongjoon-hyun / @sarutak could you please review this PR. |
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What changes were proposed in this pull request?
Fix
ExtractGeneratorto preserve aliases inside lambda functions when restructuring the plan.Previously,
ExtractGeneratorcalledtrimNonTopLevelAliaseson all expressions in the project list before extracting the generator. This stripped aliases inside lambda functions (e.g., struct(x.as("data"))) beforeCreateStructcould resolve them into struct field names.The fix uses
trimNonTopLevelAliasesonly for pattern matching (to detect generators viaAliasedGenerator), but preserves the original untrimmed expression for non-generator project items.Why are the changes needed?
When using explode together with transform in the same
select statement, aliases used inside the transformed column'sstruct()are ignored. Field names become auto-generated (x_1, x_2) instead of the user-specified alias. This only happens with the DataFrame/Dataset API, not with SQL.Does this PR introduce any user-facing change?
Yes. Struct field aliases inside transform lambdas are now correctly preserved when explode (or any generator) is in the same
select.How was this patch tested?
Added a test in
GeneratorFunctionSuiteverifying that struct field aliases are preserved when explode and transform are used together, including single and multiple aliases.Was this patch authored or co-authored using generative AI tooling?
Yes.