On Tue, May 24, 2011 at 12:14:16PM +0000, Julian Einwag - rockenstein AG wrote:
>
> I just came across the query "visible_to_system" in SystemGroup_queries.xml:
>
> SELECT MAX(DECODE(VSGM.server_id, :sid, 1, 0)) is_system_member,
> VSGM.GROUP_ID id,
> VSGM.GROUP_NAME,
> VSGM.GROUP_TYPE,
> VSGM.CURRENT_MEMBERS,
> VSGM.MAX_MEMBERS,
> DECODE(USGP.server_group_id,VSGM.group_id,1,0) AS
> USER_PERMITTED_ACCESS
> FROM rhnVisServerGroupMembership VSGM, rhnUserServerGroupPerms USGP
> WHERE VSGM.ORG_ID = :org_id
> AND :user_id = USGP.user_id (+)
> AND VSGM.group_id = USGP.server_group_id (+)
> GROUP BY VSGM.group_id, VSGM.group_name, VSGM.group_type,
> VSGM.current_members, VSGM.max_members, USGP.server_group_id
> ORDER BY UPPER(VSGM.group_name), VSGM.group_id
>
> While I do understand that (+) is the old fashioned Oracle syntax for outer
> joins, I'm having trouble understanding what the (+) does in the condition
> ':user_id = USGP.user_id (+)', since it's not join-related. I did some quick
> tests on an Oracle installation but I couldn't make sense of it.
>
> Any help would be appreciated.
Think of it as if you had
(
select :user_id from dual
)
and an outer join of this subselect with that USGP.
The
AND :user_id = USGP.user_id (+)
matches where the USGP.user_id is the same as :user_id, or where the
USGP's columns have NULL value due to the records not being present at
all.
You can try
select web_customer.id, web_contact.id
from web_customer, web_contact
where web_customer.id = web_contact.id (+)
and 1 = web_contact.id (+)
to see something similar -- on my system it returns
ID ID
---------- ----------
1 1
2
3
4
5
25
26
46
66
--
Jan Pazdziora
Principal Software Engineer, Satellite Engineering, Red Hat
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