Re: [gnome-db] GdaSqlBuiler: JOIN AS

[Murray Cumming <murrayc murrayc com>]

On Mon, 2010-05-17 at 15:02 +0200, Vivien Malerba wrote:
> On 17 May 2010 14:53, Murray Cumming <murrayc murrayc com> wrote:
> > On Mon, 2010-05-17 at 14:43 +0200, Vivien Malerba wrote:
> >> On 17 May 2010 14:39, Murray Cumming <murrayc murrayc com> wrote:
> >> > On Mon, 2010-05-17 at 14:20 +0200, Vivien Malerba wrote:
> >> >> On 17 May 2010 10:07, Murray Cumming <murrayc murrayc com> wrote:
> >> >> > In Glom, I use the AS keyword with JOINS, to allow multiple joins with
> >> >> > the same table. A simple case looks like this, though it's unnecessary
> >> >> > in this particular example:
> >> >> >
> >> >> > SELECT "albums"."album_id", "albums"."name", "albums"."artist_id",
> >> >> > "relationship_artist"."name",
> >> >> > FROM "albums"
> >> >> > LEFT JOIN "artists"
> >> >> >  AS "relationship_artist"
> >> >> >  ON ("albums"."artist_id" = "relationship_artist"."artist_id")
> >> >> > WHERE "albums"."album_id" = 123
> >> >> >
> >> >> > (That might be an "alias", but I don't know if that's the right
> >> >> > terminology.)
> >> >> >
> >> >> > But I don't see how to do that with
> >> >> > gda_sql_builder_select_join_targets()
> >> >> > http://library.gnome.org/devel/libgda/unstable/GdaSqlBuilder.html#gda-sql-builder-select-join-targets
> >> >> >
> >> >>
> >> >> To do this you need to specify an alias when using the
> >> >> gda_sql_builder_select_add_target*() methods.
> >> >
> >> > But that's for adding table targts, right? How would it know which join
> >> > the alias name is for?
> >> >
> >>
> >> The alias is for a target (table or sub select), not for a join: you
> >> don't need to name joins as they are never referenced anywhere else in
> >> the SQL statement, you can name targets if necessary.
> >
> > In my example, the join name is mentioned in the list of fields. For
> > instance, relationship_artist.name.
> >
> > Here's a silly example that shows the need for the name, because using
> > the table name would be ambiguous:
> >
> > SELECT "albums"."album_id", "albums"."name",
> > "albums"."artist_singer_id", "relationship_artist_singer"."name",
> > "albums"."artist_drummer_id", "relationship_artist_drummer"."name",
> >  FROM "albums"
> >  LEFT JOIN "artists"
> >    AS "relationship_artist_singer"
> >    ON ("albums"."artist_singer_id" =
> > "relationship_artist_singer"."artist_id")
> >  LEFT JOIN "artists"
> >    AS "relationship_artist_drummer"
> >    ON ("albums"."artist_drummer_id" =
> > "relationship_artist_drummer"."artist_id")
> > WHERE "albums"."album_id" = 123
> >
> 
> This example illustrates why you need to be able to set targets'
> aliases. In this example you have the following targets:
> A: "albums"
> B: "artists" with the "relationship_artist_singer" alias
> C: "artists" with the "relationship_artist_drummer" alias
> 
> and you reference the targets using their alias in the join condition
> and in the list of fields to be selected.
> 
> and 2 joins (joinning conditions not mentionned here):
> A <--> B
> A <--> C
> 
> the joins themselves are never referenced anywhere in the statement,
> so they are not named.

So the SQL statement would/could look different?

-- 
murrayc murrayc com
www.murrayc.com
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