SQL query to find users with certain values in another table - mysql

Question

Overview
I have two tables - tmc_users and tmc_user_usergroup_map.
In tmc_users, there is a list of user_ids and in tmc_usergroup_map each user_id can be associated with multiple group_ids.
I am trying to find all the user_ids who have a group_id of 12 but do not have a group_id of 17.
Each user can be a member of both.
Current query
This is the query to get all the users associated with the group_id 12, which returns a total number of 1439 rows:
SELECT `id`, LTRIM(RTRIM(`name`)), COUNT(`id`) AS `total`
FROM `tmc_users` u
LEFT JOIN `tmc_user_usergroup_map` g
ON u.`id` = g.`user_id`
WHERE g.`group_id` = 12
ORDER BY LTRIM(RTRIM(`name`)) ASC
New query
This is what I've tried in order to filter out users who also are in the group_id 17:
SELECT `id`, LTRIM(RTRIM(`name`)), COUNT(`id`) AS `total`
FROM `tmc_users` u
LEFT JOIN `tmc_user_usergroup_map` g
ON u.`id` = g.`user_id`
WHERE g.`group_id` != 17
AND g.`group_id` = 12
ORDER BY LTRIM(RTRIM(`name`)) ASC
However, this returns the same number of rows - 1439 - whereas the actual number of users this should have is 1353.
How can I make this work in one single query?

Answer 1

You can use NOT EXISTS:
SELECT `id`, LTRIM(RTRIM(`name`)), COUNT(`id`) AS `total`
FROM `tmc_users` u
LEFT JOIN `tmc_user_usergroup_map` g
ON u.`id` = g.`user_id`
WHERE g.`group_id` = 12 AND
NOT EXISTS (SELECT 1
FROM `tmc_user_usergroup_map` AS t
WHERE t.`user_id` = u.`id` AND t.`group_id` = 17)
ORDER BY LTRIM(RTRIM(`name`)) ASC