Обсуждение: A Not Join

I have three table:
Users - Contains username, ID etc...
Permissions - A permission name and ID
Link up table - The user.id and permission.id

If a user.id and a permission.id row exists in the linkuptable the user
have that permission granted.

With the statement below I can see the permissions a user have.

SELECT users.username, permissions.name
FROM users INNER JOIN linkuptable
  ON (users.id = linkuptable.userid)
INNER JOIN permissions
  ON (permissions.id = linkuptable.permissionid)
WHERE users.username = 'DummyUser'

How do I see the permissions that user DON'T have with a fast SQL statement.

Thus, a NOT the statement for the above SQL statement

Regards

Lani

On Tue, Nov 01, 2005 at 04:27:01PM +0200, L van der Walt wrote:
> I have three table:
> Users - Contains username, ID etc...
> Permissions - A permission name and ID
> Link up table - The user.id and permission.id
>
> If a user.id and a permission.id row exists in the linkuptable the user
> have that permission granted.
>
> With the statement below I can see the permissions a user have.
>
> SELECT users.username, permissions.name
> FROM users INNER JOIN linkuptable
>  ON (users.id = linkuptable.userid)
> INNER JOIN permissions
>  ON (permissions.id = linkuptable.permissionid)
> WHERE users.username = 'DummyUser'
>
> How do I see the permissions that user DON'T have with a fast SQL statement.
>
> Thus, a NOT the statement for the above SQL statement

LEFT JOIN permissions ON (...)
WHERE permissions.id IS NULL

You might have to do the NULL check in a HAVING clause instead... try
it.

BTW, this is probably better asked on pgsql-sql.
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Jim C. Nasby, Sr. Engineering Consultant      jnasby@pervasive.com
Pervasive Software      http://pervasive.com    work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf       cell: 512-569-9461

L van der Walt <mailing@lani.co.za> writes:

> I have three table:
> Users - Contains username, ID etc...
> Permissions - A permission name and ID
> Link up table - The user.id and permission.id
>
> If a user.id and a permission.id row exists in the linkuptable the user
> have that permission granted.
>
> With the statement below I can see the permissions a user have.
>
> SELECT users.username, permissions.name
> FROM users INNER JOIN linkuptable
>   ON (users.id = linkuptable.userid)
> INNER JOIN permissions
>   ON (permissions.id = linkuptable.permissionid)
> WHERE users.username = 'DummyUser'
>
> How do I see the permissions that user DON'T have with a fast SQL statement.
>

Simple.

select permname
from permissions
where permid not in (
    select permid
from linkage
    where userid = 'dummy'
);

Or... a slick way to get the anti-permission for the whole bunch of
users is to;

cross join the userids with permids and then EXCEPT SELECT from
linkage table to filter out the active permissions.

Have fun!


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