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* join against a function-result fails
@ 2012-07-28 01:57 Andreas <maps.on@gmx.net>
2012-07-28 02:31 ` Re: join against a function-result fails David Johnston <polobo@yahoo.com>
0 siblings, 1 reply; 2+ messages in thread
From: Andreas @ 2012-07-28 01:57 UTC (permalink / raw)
To: pgsql-sql
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_ids this 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?
^ permalink raw reply [nested|flat] 2+ messages in thread
* Re: join against a function-result fails
2012-07-28 01:57 join against a function-result fails Andreas <maps.on@gmx.net>
@ 2012-07-28 02:31 ` David Johnston <polobo@yahoo.com>
0 siblings, 0 replies; 2+ messages in thread
From: David Johnston @ 2012-07-28 02:31 UTC (permalink / raw)
To: Andreas <maps.on@gmx.net>; +Cc: pgsql-sql
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_ids this 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 recursive CTE you can start at the bottom of the trees and only evaluate the needed branches.
David J.
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2012-07-28 01:57 join against a function-result fails Andreas <maps.on@gmx.net>
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