> On 25/05/2023 06:52 CEST Laurenz Albe wrote:
>
> 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".
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:T2 (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
