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* Cross-Product JOIN?
@ 2023-05-24 08:22 Atomic_Sheep <atomic.sheep@gmail.com>
0 siblings, 1 reply; 8+ messages in thread
From: Atomic_Sheep @ 2023-05-24 08:22 UTC (permalink / raw)
To: pgsql-docs@lists.postgresql.org
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?
^ permalink raw reply [nested|flat] 8+ messages in thread
* Re: Cross-Product JOIN?
@ 2023-05-24 13:46 Erik Wienhold <ewie@ewie.name>
parent: Atomic_Sheep <atomic.sheep@gmail.com>
0 siblings, 1 reply; 8+ messages in thread
From: Erik Wienhold @ 2023-05-24 13:46 UTC (permalink / raw)
To: Atomic_Sheep <atomic.sheep@gmail.com>; pgsql-docs@lists.postgresql.org
> On 24/05/2023 10:22 CEST Atomic_Sheep <atomic.sheep@gmail.com> 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
^ permalink raw reply [nested|flat] 8+ messages in thread
* Re: Cross-Product JOIN?
@ 2023-05-24 19:10 Erik Wienhold <ewie@ewie.name>
parent: Erik Wienhold <ewie@ewie.name>
0 siblings, 2 replies; 8+ messages in thread
From: Erik Wienhold @ 2023-05-24 19:10 UTC (permalink / raw)
To: Atomic_Sheep <atomic.sheep@gmail.com>; pgsql-docs@lists.postgresql.org
> On 24/05/2023 15:46 CEST Erik Wienhold <ewie@ewie.name> 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.
--
Erik
Attachments:
[text/x-patch] 0001-Use-Cartesian-product-consistently-in-docs.patch (1.6K, ../../2053109544.160895.1684955437950@office.mailbox.org/2-0001-Use-Cartesian-product-consistently-in-docs.patch)
download | inline diff:
From b23bd267ac9c4e79efb472c08dc35737bc8e9ca6 Mon Sep 17 00:00:00 2001
From: Erik Wienhold <ewie@ewie.name>
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 <replaceable>table_reference</replaceable> <optional>, <replaceable>table_r
input tables. As with <literal>USING</literal>, these columns appear
only once in the output table. If there are no common
column names, <literal>NATURAL JOIN</literal> behaves like
- <literal>JOIN ... ON TRUE</literal>, producing a cross-product join.
+ <literal>CROSS JOIN</literal>.
</para>
<note>
@@ -1362,7 +1362,7 @@ GROUPING SETS (
<para>
If multiple grouping items are specified in a single <literal>GROUP BY</literal>
- 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:
<programlisting>
GROUP BY a, CUBE (b, c), GROUPING SETS ((d), (e))
--
2.40.1
^ permalink raw reply [nested|flat] 8+ messages in thread
* Re: Cross-Product JOIN?
@ 2023-05-25 04:52 Laurenz Albe <laurenz.albe@cybertec.at>
parent: Erik Wienhold <ewie@ewie.name>
1 sibling, 1 reply; 8+ messages in thread
From: Laurenz Albe @ 2023-05-25 04:52 UTC (permalink / raw)
To: Erik Wienhold <ewie@ewie.name>; Atomic_Sheep <atomic.sheep@gmail.com>; pgsql-docs@lists.postgresql.org
On Wed, 2023-05-24 at 21:10 +0200, Erik Wienhold wrote:
> > On 24/05/2023 15:46 CEST Erik Wienhold <ewie@ewie.name> 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
^ permalink raw reply [nested|flat] 8+ messages in thread
* Re: Cross-Product JOIN?
@ 2023-05-25 06:59 Erik Wienhold <ewie@ewie.name>
parent: Laurenz Albe <laurenz.albe@cybertec.at>
0 siblings, 1 reply; 8+ messages in thread
From: Erik Wienhold @ 2023-05-25 06:59 UTC (permalink / raw)
To: Laurenz Albe <laurenz.albe@cybertec.at>; pgsql-docs@lists.postgresql.org
> On 25/05/2023 06:52 CEST Laurenz Albe <laurenz.albe@cybertec.at> wrote:
>
> On Wed, 2023-05-24 at 21:10 +0200, Erik Wienhold wrote:
> > > On 24/05/2023 15:46 CEST Erik Wienhold <ewie@ewie.name> 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".
Cross product can mean Cartesian product depending on the context. [0]
> Since we are talking about Cartesian products: is the term "Cartesian join"
> used anywhere?
Not in the docs:
$ git grep -iw cartesian -- doc
doc/src/sgml/cube.sgml: the lower-dimensional one is assumed to be a Cartesian projection, i. e., having zeroes
doc/src/sgml/perform.sgml: would be inefficient, since the full Cartesian product of A and C
doc/src/sgml/planstats.sgml: Cartesian product of the two inputs, multiplied by the
doc/src/sgml/queries.sgml: (that is, the Cartesian product of their rows is formed; see below).
doc/src/sgml/queries.sgml: <replaceable>T2</replaceable> (i.e., a Cartesian product),
doc/src/sgml/ref/select.sgml: specified, the result is the Cartesian product (cross join) of all
doc/src/sgml/ref/select.sgml: Cartesian product.
doc/src/sgml/ref/select.sgml: Cartesian product (i.e., all combined rows that pass its join
doc/src/sgml/ref/select.sgml: They produce a simple Cartesian product, the same result as you get from
but in a few comments:
$ git grep -i 'cartesian\(\s\+join\|\s*$\)'
src/backend/optimizer/geqo/geqo_eval.c: * a cartesian join to be performed. When force is false, do only
src/backend/optimizer/path/joinrels.c: * upper level, we must be willing to make a cartesian join of a and b;
src/backend/optimizer/path/joinrels.c: * cartesian joins in this case (no bushy).
src/test/regress/expected/join.out:-- test for ability to use a cartesian join when necessary
src/test/regress/sql/join.sql:-- test for ability to use a cartesian join when necessary
[0] https://mathworld.wolfram.com/CartesianProduct.html
--
Erik
^ permalink raw reply [nested|flat] 8+ messages in thread
* Re: Cross-Product JOIN?
@ 2023-05-25 21:46 Laurenz Albe <laurenz.albe@cybertec.at>
parent: Erik Wienhold <ewie@ewie.name>
0 siblings, 1 reply; 8+ messages in thread
From: Laurenz Albe @ 2023-05-25 21:46 UTC (permalink / raw)
To: Erik Wienhold <ewie@ewie.name>; pgsql-docs@lists.postgresql.org
On Thu, 2023-05-25 at 08:59 +0200, Erik Wienhold wrote:
> > Since we are talking about Cartesian products: is the term "Cartesian join"
> > used anywhere?
>
> Not in the docs:
I was trying to be funny. The Cartesian product of {Cartesian,cross} and
{product,join} would be {Cartesian product,Cartesian join,cross product,cross join}.
Yours,
Laurenz Albe
^ permalink raw reply [nested|flat] 8+ messages in thread
* Re: Cross-Product JOIN?
@ 2023-05-25 23:23 Erik Wienhold <ewie@ewie.name>
parent: Laurenz Albe <laurenz.albe@cybertec.at>
0 siblings, 0 replies; 8+ messages in thread
From: Erik Wienhold @ 2023-05-25 23:23 UTC (permalink / raw)
To: Laurenz Albe <laurenz.albe@cybertec.at>; pgsql-docs@lists.postgresql.org
> On 25/05/2023 23:46 CEST Laurenz Albe <laurenz.albe@cybertec.at> wrote:
>
> On Thu, 2023-05-25 at 08:59 +0200, Erik Wienhold wrote:
> > > Since we are talking about Cartesian products: is the term "Cartesian join"
> > > used anywhere?
> >
> > Not in the docs:
>
> I was trying to be funny. The Cartesian product of {Cartesian,cross} and
> {product,join} would be {Cartesian product,Cartesian join,cross product,cross join}.
And someone beat you to it and apparently planted the joke in the codebase.
(Good one, but unfortunately hard to tell apart from a serious question.)
--
Erik
^ permalink raw reply [nested|flat] 8+ messages in thread
* Re: Cross-Product JOIN?
@ 2023-09-07 19:48 Bruce Momjian <bruce@momjian.us>
parent: Erik Wienhold <ewie@ewie.name>
1 sibling, 0 replies; 8+ messages in thread
From: Bruce Momjian @ 2023-09-07 19:48 UTC (permalink / raw)
To: Erik Wienhold <ewie@ewie.name>; +Cc: Atomic_Sheep <atomic.sheep@gmail.com>; pgsql-docs@lists.postgresql.org
On Wed, May 24, 2023 at 09:10:37PM +0200, Erik Wienhold wrote:
> > On 24/05/2023 15:46 CEST Erik Wienhold <ewie@ewie.name> 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.
Patch applied to master, thanks.
--
Bruce Momjian <bruce@momjian.us> https://momjian.us
EDB https://enterprisedb.com
Only you can decide what is important to you.
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-- links below jump to the message on this page --
2023-05-24 08:22 Cross-Product JOIN? Atomic_Sheep <atomic.sheep@gmail.com>
2023-05-24 13:46 ` Erik Wienhold <ewie@ewie.name>
2023-05-24 19:10 ` Erik Wienhold <ewie@ewie.name>
2023-05-25 04:52 ` Laurenz Albe <laurenz.albe@cybertec.at>
2023-05-25 06:59 ` Erik Wienhold <ewie@ewie.name>
2023-05-25 21:46 ` Laurenz Albe <laurenz.albe@cybertec.at>
2023-05-25 23:23 ` Erik Wienhold <ewie@ewie.name>
2023-09-07 19:48 ` Bruce Momjian <bruce@momjian.us>
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