MySQL Many-To-Many Select

Question

Still learning the MySQL ropes and I'm trying to find out how to do a specific selection involving many-to-many. I apologize if the table names are too generic, I was just doing some self-made exercises. I try my best to be a self-learner.

I have 3 tables one of which is a linking table. How do I write the statement which says "Show which users own both an HTC and a Samsung phone" (they own 2 phones). I'm guessing the answer is in the WHERE statement but I can't figure out how to word it.

-- Table: mark3
+---------+-----------+
| phoneid | name      |
+---------+-----------+
|       1 | HTC       |
|       2 | Nokia     |
|       3 | Samsung   |
|       4 | Motorolla |
+---------+-----------+

-- Table: mark4
+------+---------+
| uid  | phoneid |
+------+---------+
|    1 |       1 |
|    1 |       2 |
|    2 |       1 |
|    2 |       3 |
|    2 |       4 |
|    3 |       1 |
|    3 |       3 |
+------+---------+

-- Table: mark5
+------+-------+
| uid  | name  |
+------+-------+
|    1 | John  |
|    2 | Paul  |
|    3 | Peter |
+------+-------+

Answer 1

The key is in the GROUP BY/HAVING using a COUNT of DISTINCT phone names. When the count is 2, you'll know the user has both phones.

SELECT m5.name
    FROM mark5 m5
        INNER JOIN mark4 m4
            ON m5.uid = m4.uid
        INNER JOIN mark3 m3
            ON m4.phoneid = m3.phoneid
    WHERE m3.name in ('HTC', 'Samsung')
    GROUP BY m5.name
    HAVING COUNT(DISTINCT m3.name) = 2;