Re: join against a function-result fails

On Jul 27, 2012, at 21:57, Andreas <maps.on@gmx.net> wrote
> Hi,
> I have a table with user ids and names.
> Another table describes some rights of those users and still another one describes who inherits rights from who.
>
> A function all_rights ( user_id ) calculates all rights of a user recursively and gives back a table with all
userright_idsthis user directly has or inherits of other users as ( user_id, userright_id ). 
>
> Now I'd like to find all users who have the right 42.
>
>
> select  user_id, user_name
> from    users
>    join  all_rights ( user_id )  using ( user_id )
> where  userright_id = 42;
>
> won't work because the parameter user_id for the function all_rights() is unknown when the function gets called.
>
> Is there a way to do this?
>

Suggest you write a recursive query that does what you want.  If you really want to do it this way you can:

With cte as (Select user_id, user_name, all_rights(user_id) as rightstbl)
Select * from cte where (rightstbl).userright_id = 42;

This is going to be very inefficient since you enumerate every right for every user before applying the filter.  With a
recursiveCTE you can start at the bottom of the trees and only evaluate the needed branches. 

David J.