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
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