On Tue, 2012-07-17 at 20:06 -0300, Daniel Serodio (lists) wrote:
> Nelson A. de Oliveira wrote:
> > Hi!
> >
> > On Tue, Jul 17, 2012 at 7:36 PM, Daniel Serodio (lists)
> > <daniel.lists@mandic.com.br> wrote:
> >> I'm using pgAdmin 1.14.3, and its Graphical Query Builder generates WHERE
> >> clauses for joins. It would be nice if it generated JOIN clauses instead.
> >
> > Is there any kind of difference between WHERE or JOINs in PostgreSQL?
> > Aren't they all a cartesian product internally?
> They may be implemented the same way in PostgresSQL,
They are.
> but they're two different concepts.
How so?
> Because of this, I find it a lot easier to
> understand a complex query when the joins are in a JOIN clause.
>
I do agree here.
> In more practical terms, it's easier to change "a JOIN b ON a.pk = b.fk"
> to "a LEFT JOIN b ON a.pk = b.fk" (just have to type the LEFT keyword,
> regardless of which tables/columns are used) then change "WHERE a.pk =
> b.fk" to "WHERE a.pk = b.fk OR b.fk IS NULL" (have to add "OR b.fk IS
> NULL", which changes according to which tables/columns are used).
>
Yes, and it's less risky. If you use a JOIN, you have to add a ON clause
if you don't want to get a syntax error. That protects you from
cartesian product.
To get back on the request, that could be interesting to do, and
probably not hard.
--
Guillaume
http://blog.guillaume.lelarge.info
http://www.dalibo.com
