Cross-Product JOIN?
Hi, I'm reading the documentation and I'm trying to wrap my head around this statement: "Finally, NATURAL is a shorthand form of USING: it forms a USING list consisting of all column names that appear in both input tables. As with USING, these columns appear only once in the output table. If there are no common column names, NATURAL JOIN behaves like JOIN ... ON TRUE, producing a cross-product join." Did it mean cartesian product and not cross-product?
Re: Cross-Product JOIN?
> On 24/05/2023 10:22 CEST Atomic_Sheep wrote: > > "Finally, NATURAL is a shorthand form of USING: it forms a USING list > consisting of all column > names that appear in both input tables. As with USING, these columns > appear only once in the > output table. If there are no common column names, NATURAL JOIN > behaves like JOIN ... > ON TRUE, producing a cross-product join." > > Did it mean cartesian product and not cross-product? Cross product means cartesian product in this context. So technically correct. Personally, I think it should read cartesian product because cross product is an overloaded term and cartesian product is used more often in the documentation overall. But the same page [0] also uses cross product when talking about grouping sets. The source code uses cross product in a couple of comments, though. [0] https://www.postgresql.org/docs/15/queries-table-expressions.html -- Erik
Re: Cross-Product JOIN?
> On 24/05/2023 15:46 CEST Erik Wienhold wrote: > > Personally, I think it should read cartesian product because cross product is > an overloaded term and cartesian product is used more often in the > documentation > overall. > > But the same page [0] also uses cross product when talking about grouping > sets. > > [0] https://www.postgresql.org/docs/15/queries-table-expressions.html Here's a patch that fixes those two places. -- ErikFrom b23bd267ac9c4e79efb472c08dc35737bc8e9ca6 Mon Sep 17 00:00:00 2001 From: Erik Wienhold Date: Wed, 24 May 2023 20:21:47 +0200 Subject: [PATCH] Use Cartesian product consistently in docs Fixes two places in the docs that use "cross product" instead of the more common "Cartesian product", used throughout the rest of the docs. For the NATURAL JOIN without common column names it is easiest to refer to CROSS JOIN which is already described as the Cartesian product. --- doc/src/sgml/queries.sgml | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/doc/src/sgml/queries.sgml b/doc/src/sgml/queries.sgml index 6986ec5c92..a75a241d62 100644 --- a/doc/src/sgml/queries.sgml +++ b/doc/src/sgml/queries.sgml @@ -392,7 +392,7 @@ FROM table_reference , table_r input tables. As with USING, these columns appear only once in the output table. If there are no common column names, NATURAL JOIN behaves like -JOIN ... ON TRUE, producing a cross-product join. +CROSS JOIN. @@ -1362,7 +1362,7 @@ GROUPING SETS ( If multiple grouping items are specified in a single GROUP BY -clause, then the final list of grouping sets is the cross product of the +clause, then the final list of grouping sets is the Cartesian product of the individual items. For example: GROUP BY a, CUBE (b, c), GROUPING SETS ((d), (e)) -- 2.40.1
Re: Cross-Product JOIN?
On Wed, 2023-05-24 at 21:10 +0200, Erik Wienhold wrote: > > On 24/05/2023 15:46 CEST Erik Wienhold wrote: > > > > Personally, I think it should read cartesian product because cross product > > is > > an overloaded term and cartesian product is used more often in the > > documentation > > overall. > > > > But the same page [0] also uses cross product when talking about grouping > > sets. > > > > [0] https://www.postgresql.org/docs/15/queries-table-expressions.html > > Here's a patch that fixes those two places. +1 "Cross product" seems to be a misbegotten hybrid of "cross join" and "Cartesian product". Since we are talking about Cartesian products: is the term "Cartesian join" used anywhere? Yours, Laurenz Albe
