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2017年1月23日 14:38:36 +0000 (09:38 -0500)

Joining three tables only takes two join nodes. I think when I (tgl)
wrote this, I was envisioning possible additional joins; but since the
example doesn't show any fourth table, it's just confusing to write
a third join node.

Etsuro Fujita

Discussion: https://postgr.es/m/e6cfbaa3-af02-1abc-c25e-8fa5c6bc4e21@lab.ntt.co.jp

src/backend/optimizer/README patch | blob | blame | history

diff --git a/src/backend/optimizer/README b/src/backend/optimizer/README

index 7ae2b74b2c2d2970e925b45f32741bbc8ca24b9a..fc0fca41071228cdd734693fc0e500f562c7c392 100644 (file)

--- a/src/backend/optimizer/README

+++ b/src/backend/optimizer/README

@@ -757,9 +757,8 @@ to create a plan like

-> Seq Scan on SmallTable1 A

NestLoop

-> Seq Scan on SmallTable2 B

- NestLoop

- -> Index Scan using XYIndex on LargeTable C

- Index Condition: C.X = A.AID and C.Y = B.BID

+ -> Index Scan using XYIndex on LargeTable C

+ Index Condition: C.X = A.AID and C.Y = B.BID

so we should be willing to pass down A.AID through a join even though

there is no join order constraint forcing the plan to look like this.

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