Re: syntax for updating an aliased table

Andy Chambers wrote:
> I'm confused about the correct syntax for updating an aliased table.  I want
> to update triple from triple_updates
> where the data is different and tried to use the following....
>
> update triple old
>                            set
>                               old.obln = new.obln,  old.ointv = new.ointv,
>  old.otime = new.otime,  old.oflt = new.oflt,  old.ostr = new.ostr,
>  old.oint = new.oint,  old.oda = new.oda,  old.uasid = new.uasid
>                            from triple_update as new
>                           where (old.s = new.s and
>                                  old.g = new.g) and
>                                 ( old.obln <> new.obln or  old.ointv <>
> new.ointv or  old.otime <> new.otime or  old.oflt <> new.oflt or  old.ostr
> <> new.ostr or  old.oint <> new.oint or  old.oda <> new.oda or  old.uasid <>
> new.uasid)
>
>
> ...but postgres complains about not having column "old" in the triple table.
>  Putting an "as" between triple and old on the first line didn't make any
> difference.  If
> I leave out the old alias, it complains about the columns being ambiguous.
>  How should the query above be changed to be syntactically correct?

Don't use the table alias (or name for that matter) on the left-hand side of
the assignments, so:

  update triple old
     set obln = new.obln,
         ointv = new.ointv,
         ...
     from triple_update as new
     where (old.s = new.s and old.g = new.g) and ...

The update statement already unambiguously defines what table is being updated
and the target columns are all that are necessary in the assignments.

HTH

Bosco.