> 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?
A quick way is with a temp table, eg ...
DROP TEMPORARY TABLE IF EXISTS j;
CREATE TEMPORARY TABLE j
FROM users u
LEFT JOIN usergroups u USING (userID);
SELECT j.partyID AS NotGroup1
LEFT JOIN usergroups ug
ON j.userID=ug.userID AND ug.groupID=1
WHERE ug.group IS NULL;
DROP TEMPORARY TABLE j;
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