Re: not grokking outer joins...

On Mon, 20 Aug 2001, will trillich wrote:

> i'm trying to wrap outer joins around my cerebellum:
>
>     CUST:
>         id serial
>         name varchar(30)
>     ITEM:
>         cust integer references cust (id)
>         data varchar(30)
>     INFO:
>         cust integer references cust (id)
>         stuff text
>
> for my query i'd like, for every customer, to have
> item.* show up if it exists, and info.* show up
> if it exists...
>
>     select
>         CUST.name,
>         ITEM.data,
>         INFO.stuff
>     from
>         CUST left join ITEM on (CUST.id=ITEM.cust),
>         CUST left join INFO on (CUST.id=INFO.cust)
>     .... not!
>
> or does this need some subselect magic?
>

I think
from
cust left join item on (cust.id=item.cust) left join
 info on (cust.id=info.cust)

might be what you want.

> and (separate question) is there a way to be sure that ONE or the
> OTHER or BOTH have joinable data, but don't show CUST if neither
> ITEM nor INFO has a match?
>
>     foreach CUST
>         if ITEM matches
>             show record
>         elsif INFO matches
>             show record
>         else -- neither matches
>             dont show squat, not even from cust
>         end if
>     end foreach

I'd say something like "where item.cust is not null or
info.cust is not null"