Обсуждение: Union instead of Outer Join

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Union instead of Outer Join

От
"Unnikrishnan Menon"
Дата:
Hi,
 
I have this query in oracle which I'am trying to port to PostgreSQL :
 
Select
    item_code, nvl(user_id,' ') as user_id
from
    item_list L, User_detail B, User_detail S
where
    L.user_id = S.User_id and
    L.other_userid = B.user_id(+) and
    L.item_code = 1234;
 
This query gives me 1 row as result. L.other_userid could be null.
 
I try changing the query thus in postgreSQL :
 
Select
    item_code, nvl(user_id,' ') as user_id
from
    item_list L, User_detail B, User_detail S
where
    L.user_id = S.User_id and
    L.other_userid = B.user_id and
    L.item_code = 1234
Union
Select
    item_code, nvl(user_id,' ') as user_id
from
    item_list L, User_detail B, User_detail S
where
    L.user_id = S.User_id and
    L.item_code = 1234 and
    0 = ( Select
                 count(*)
            from
                 listed_items L, user_detail B, user_detail S
            where
                L.other_userid = B.user_id);
 
The above query does not return any row. Where could I be going wrong?
 
Any help would be appreciated.
 
Thanx in advance
 
Unni

Re: Union instead of Outer Join

От
Jeff Eckermann
Дата:
select   item_code, coalesce(user_id, ' ') as user_id
from   item_list l inner join user_detail s on l.user_id
= s.user_id   left outer join  user_detail b on l.other_userid =
b.user_id
where   l.item_code = 1234;

Joins can be named in different ways; see the "SELECT"
page in the "SQL Commands" section of the docs.

Your message suggests that you want a right join on b
& l; the syntax above corresponds to what you stated
(per my Oracle reference).

--- Unnikrishnan Menon
<unnikrishnan.menon@chennai.transys.net> wrote:
> Hi,
> 
> I have this query in oracle which I'am trying to
> port to PostgreSQL :
> 
> Select 
>     item_code, nvl(user_id,' ') as user_id 
> from 
>     item_list L, User_detail B, User_detail S
> where 
>     L.user_id = S.User_id and
>     L.other_userid = B.user_id(+) and
>     L.item_code = 1234;
> 
> This query gives me 1 row as result. L.other_userid
> could be null.
> 
> I try changing the query thus in postgreSQL :
> 
> Select 
>     item_code, nvl(user_id,' ') as user_id 
> from 
>     item_list L, User_detail B, User_detail S
> where 
>     L.user_id = S.User_id and
>     L.other_userid = B.user_id and
>     L.item_code = 1234
> Union
> Select 
>     item_code, nvl(user_id,' ') as user_id 
> from 
>     item_list L, User_detail B, User_detail S
> where 
>     L.user_id = S.User_id and
>     L.item_code = 1234 and
>     0 = ( Select 
>                  count(*) 
>             from 
>                  listed_items L, user_detail B,
> user_detail S
>             where 
>                 L.other_userid = B.user_id);
> 
> The above query does not return any row. Where could
> I be going wrong?
> 
> Any help would be appreciated.
> 
> Thanx in advance
> 
> Unni
> 


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Re: Union instead of Outer Join

От
Bruno Wolff III
Дата:
On Thu, Jan 17, 2002 at 09:12:17PM +0530, Unnikrishnan Menon <unnikrishnan.menon@chennai.transys.net> wrote:
> Any help would be appreciated.

If you are running 7.1 or can upgrade to 7.1, then you can do outer joins
and don't need to use the union trick.