Обсуждение: "=" or ":=" ?

    Hello,

    I'm trying to optimize assign_vertex_id() function provided by
pgRouting/PostGIS. In this function, I can see :

DECLARE
       points record;
       i record;
       source_id int;
       target_id int;
       pre varchar;
       post varchar;

       srid integer;

       BEGIN

        BEGIN
            DROP TABLE vertices_tmp;
             EXCEPTION
            WHEN UNDEFINED_TABLE THEN
                 END;

        EXECUTE 'CREATE TABLE vertices_tmp (id serial)';

        FOR i IN EXECUTE 'SELECT srid FROM geometry_columns WHERE
f_table_name='''|| quote_ident(geom_table)||'''' LOOP
        END LOOP;

        srid := i.srid;

        EXECUTE 'SELECT addGeometryColumn(''vertices_tmp'', ''the_geom'',
'||srid||', ''POINT'', 2)';


                 CREATE INDEX vertices_tmp_idx ON vertices_tmp USING
GIST (the_geom);

                 pre = '';
                 post = '';

    I don't understand last assignations. In pgsql documentation, ther is
written that all assignations have to be written with ":=", not with
"=". What is the difference between "=" and ":=" ? I don't find any
information about "=".

    Regards,

    JKB

BERTRAND Joël wrote:

>     I don't understand last assignations. In pgsql documentation, ther is
> written that all assignations have to be written with ":=", not with
> "=". What is the difference between "=" and ":=" ? I don't find any
> information about "=".

It's exactly the same.  := is the documented way, but = is also
accepted and behaves identically.

--
Alvaro Herrera                                http://www.CommandPrompt.com/
PostgreSQL Replication, Consulting, Custom Development, 24x7 support

=?ISO-8859-1?Q?BERTRAND_Jo=EBl?= <joel.bertrand@systella.fr> writes:
> What is the difference between "=" and ":=" ?

None; plpgsql accepts either for assignment.

            regards, tom lane

Tom Lane wrote:
> =?ISO-8859-1?Q?BERTRAND_Jo=EBl?= <joel.bertrand@systella.fr> writes:
>> What is the difference between "=" and ":=" ?
>
> None; plpgsql accepts either for assignment.

    Thank you for your answer. I suggest to add a note in documentation ;-)

    Regards,

    JKB

On Thu, 2008-02-28 at 20:11 +0100, BERTRAND Joël wrote:
> Tom Lane wrote:
> > =?ISO-8859-1?Q?BERTRAND_Jo=EBl?= <joel.bertrand@systella.fr> writes:
> >> What is the difference between "=" and ":=" ?
> >
> > None; plpgsql accepts either for assignment.
>
>     Thank you for your answer. I suggest to add a note in documentation ;-)

I think that it is undocumented on purpose.

"=" in SQL is generally for testing equality, and having one operator
mean two completely different things can be confusing. Therefore, ":="
is encouraged.

Regards,
    Jeff Davis