Capture global ORDER BY requirement under ScalarSubqueryExec root#23146
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Capture global ORDER BY requirement under ScalarSubqueryExec root#23146sgrebnov wants to merge 1 commit into
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require_top_ordering_helper bailed on ScalarSubqueryExec because it has multiple children (main input + subquery plans), so the rule stamped an empty OutputRequirementExec (order_by=[], dist_by=Unspecified) at the root and never recorded the query's global ORDER BY requirement. Descend through child 0 (the order-transparent main input: maintains_input_order()[0] == true, no required input ordering) to find and protect the top SortExec, reattaching the subquery children unchanged.
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Which issue does this PR close?
After upgrading from DataFusion 53 to 54 queries with ScalarSubquery started returning unordered results (
ORDER BYwas not respected)Rationale for this change
OutputRequirementswalks the plan viarequire_top_ordering_helperto capture the query's globalORDER BYas anOutputRequirementExec. The helper bails on any node with more than one child (children.len() != 1).ScalarSubqueryExecis such a node — child 0 is the order-transparent main input and the rest are uncorrelated subquery plans — so when it is the plan root the rule stops immediately and stamps an emptyOutputRequirementExec(order_by=[], dist_by=Unspecified)at the top, never recording the global ordering requirement.ScalarSubqueryExecis order-transparent on its main input (maintains_input_order()[0] == true, no required input ordering), so the search should descend through child 0, as it does for other single-child order-preserving operators.What changes are included in this PR?
require_top_ordering_helpernow special-casesScalarSubqueryExec: it descends through child 0 to find and wrap the topSortExec, reattaching the subquery children unchanged.Are these changes tested?
A new unit test (
add_mode_descends_through_scalar_subquerythat asserts theOutputRequirementExeccarrying the real ordering is placed below theScalarSubqueryExec; without the fix the rule produces the emptyorder_by=[], dist_by=Unspecifiedrequirement at the root.Existing
subquery.slt/ TPC-H plan snapshots are unchanged: for built-in sourcesEnforceSortingindependently rebuilds the order-preserving merge, so final plans are identical. WIP: adding visible/end-to-end coverage on top of the unit test.Are there any user-facing changes?
No.