gerald_clark wrote:
>>
>>
>>> I've checked the archives and found an explanation as to how the
>>> check if a record is not in a many-to-many table. The answer to
>>> that is somewhat simple and clear to me. But here's my problem: how
>>> do you check if a record doesn't have a *particular* many-to-many
>>> relationship? As in, let's say I have three tables: users, groups,
>>> and users_groups linking the two in a many-to-many relationship.
>>> Now let's say that I want to select all users who are not in the
>>> group "Group1" -- that is, that user may have entries in the
>>> users_groups table, but they would be for other groups, not "Group1."
>>>
>>> One more thing: this is easily done with subqueries, but for
>>> performance reasons, I need to do it with explicit joins. Anyone
>>> know how I can do this?
>>
>
> SELECT u.userID
> FROM users u
> LEFT JOIN user_groups ug
> ON u.userID = ug.userID and ug.groupID = 'Group1'
> WHERE ug.groupID IS NULL
>
>
But I have three tables, not two. In other words, I have the name
'Group1,' but not the id.
--
Marco Carbone
Webmaster/Web Developer
Committee to Regulate and Control Marijuana
http://www.regulatemarijuana.org
