fix: inherit field names from left projection in set expressions when missing#20819
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gruuya wants to merge 1 commit intoapache:mainfrom
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fix: inherit field names from left projection in set expressions when missing#20819gruuya wants to merge 1 commit intoapache:mainfrom
gruuya wants to merge 1 commit intoapache:mainfrom
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… missing Otherwise they might end up having the same column names, which is prohibited. This is only the case for literals, other expression types should have default unique names.
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Which issue does this PR close?
Rationale for this change
DataFusion requires all projected expressions to have unique names during planning, so it doesn't support
select 0, 0for instance.However this shouldn't be an issue when this is just a sub-SELECT in a larger query which does abide by this rule. For example a set expression (UNION, EXCEPT, INTERSECT) query should only require the first SELECT to provide a unique schema, and that should be sufficient.
Furthermore, this requirement is even more redundant, since all field name/aliases other than those in the first SELECT are discarded anyway.
What changes are included in this PR?
For set expression queries, alias all unnamed right-hand side projection expressions based on the left-hand side column names.
This is only done in the case for literals, other expression types should have default unique names.
Are these changes tested?
Yes, there are SQL->plan tests as well as SLT tests added.
Are there any user-facing changes?