SQL multiple inclusive joins - sql

Question

Below is schema description. I would like to construct a query that for a given user will return all the cases that are shared directly via case_users OR indirectly via case_groups table. Here is my attempt, where I pull the groups the user belongs to upfront:
SELECT * FROM `cases`
INNER JOIN `case_users` ON `cases`.`id` = `case_users`.`case_id`
INNER JOIN `case_groups` ON `cases`.`id` = `case_groups`.`case_id`
WHERE `case_users`.`user_id` = '<USER_ID>'
OR `case_groups`.`group_id` IN (<USER_GROUP_LIST>)
EXPLAIN returns the following: Impossible WHERE noticed after reading const table...
How can I get it done? Ideally I would like to retrieve all the cases in a single shot - without pulling the USER_GROUP_LIST - groups that the user belongs to.
mysql> describe users;
+-------------+--------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------------+--------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
+-------------+--------------+------+-----+---------+----------------+
mysql> describe cases;
+-------------+--------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------------+--------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
+-------------+--------------+------+-----+---------+----------------+
mysql> describe case_users;
+-------------+---------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------------+---------+------+-----+---------+-------+
| user_id | int(11) | NO | PRI | NULL | |
| case_id | int(11) | NO | PRI | NULL | |
+-------------+---------+------+-----+---------+-------+
mysql> describe case_groups;
+-------------+---------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------------+---------+------+-----+---------+-------+
| case_id | int(11) | NO | PRI | NULL | |
| group_id | int(11) | NO | PRI | NULL | |
+-------------+---------+------+-----+---------+-------+
mysql> describe group_users;
+-------------+---------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------------+---------+------+-----+---------+-------+
| group_id | int(11) | NO | PRI | NULL | |
| user_id | int(11) | NO | PRI | NULL | |
+-------------+---------+------+-----+---------+-------+

Answer 1

Your joins will only return cases whose Id is in both the case_users and case_groups..
If its one or the other, then you need 2 queries, which you can UNION to get all the results in a single resultset:
SELECT `cases`.* FROM `cases`
INNER JOIN `case_users` ON `cases`.`id` = `case_users`.`case_id`
WHERE `case_users`.`user_id` = '<USER_ID>'
UNION
SELECT `cases`.* FROM `cases`
INNER JOIN `case_groups` ON `cases`.`id` = `case_groups`.`case_id`
WHERE `case_groups`.`group_id` IN (SELECT `group_users`.`group_id`
FROM `group_users`
WHERE `group_users`.`user_id` = '<USER_ID>')