--- Andre Schubert <andre@km3.de> wrote:
> Hi all,
>
> i need help to build a select query or
> plpgsql-fucntion
> for the following tables.
>> Is it possible to build a select query that selects
> d.name for each a.name where
> a.id = b.a_id and d.id = c.d_id and each b.c_id must
> exist in c.b_id.
>
> Example:
> a: b: c : d:
> id | name a_id | c_id b_id | d_id id |
> name
> ----|------- -------|----- -------|-----
> -----|--------
> 1 | A_Name1 1 | 1 1 | 1 1 |
> D_Name1
> 2 | A_Name2 1 | 2 2 | 1 2 |
> D_Name2
> 3 | A_Name3 2 | 1 3 | 2 3 |
> D_Name3
> 4 | A_Name4 3 | 3 4 | 2
> 3 | 4 5 | 3
> 4 | 5
>
> i wish to have to following result:
> --------|--------
> A_Name1 | D_Name1
> A_Name3 | D_Name2
> A_Name4 | D_Name3
>
> I hope someone could understand the problem
You can use views to to simplify complicated queries
Create a view that will join table A & B
Create view view_ab(name,id) as
select name,c_id
from a,b
where id = c_id;
Create a view that will join table C & D
Create view view_cd(name2,id2) as
select name,b_id
from c,d
where id=d_id;
Create a query that will join the views "view_ab" and
"view_cd"
Select name,name2
from view_ab,view_cd
where id=id2;
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