docs(RETURN): document pattern expressions in projections#364
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gregfelice wants to merge 1 commit into
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docs(RETURN): document pattern expressions in projections#364gregfelice wants to merge 1 commit into
gregfelice wants to merge 1 commit into
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Pattern expressions (path patterns such as (a)-[:KNOWS]->(:Person)) can be used directly in a RETURN/WITH projection, not only as WHERE predicates. Adds a worked example to the RETURN reference with verified output, plus a performance note: a pattern expression is evaluated as an EXISTS subquery once per result row, so its cost scales with the number of rows projected. Documents the projection capability added in apache/age#2360.
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What — Documents that pattern expressions (path patterns such as
(a)-[:KNOWS]->(:Person)) can be returned directly from aRETURN/WITHprojection, not only used asWHEREpredicates. Adds a worked example to the RETURN reference with verified output, plus a performance note.Why — Follow-up to the review of apache/age#2360. The reviewer asked that the per-row
EXISTS-subquery cost of pattern expressions in projection contexts be discoverable from the Cypher reference, not just the PR history.Performance note — A pattern expression is evaluated as an
EXISTSsubquery, once per result row in a projection, so cost scales with rows projected. The note makes only this mechanically-grounded claim.Depends on apache/age#2360 (the projection capability); should not merge before it.
Verification — Example output generated against a PG18 build of the #2360 branch using the canonical doc graph (
intro/aggregation.md).