Inserting rows into a MySQL DB based on what is missing - mysql

Question

I've this table called Runks (a Runk is basically like a challenge in this game that I'm making).
Every game can hold 4 users. Thus per round 4 Runks will be created. 1 round will last 24 hours.
At the end of the round the status of these Runks changes.
However I am running into a problem. If one or more of the users neglected to upload Runk in the meantime I need to create an empty Runk for them in the database.
This query:
SELECT runk_group_id, COUNT(runk_id)
FROM runks
WHERE runk_status = 'ACTIVE'
GROUP BY runk_group_id
Would output this:
This should then result in a next query creating 5 Runks.
1 Runk needs to be created for group_id 32
1 Runk needs to be created for group_id 35
3 Runks need to be created for group_id 44
Also one thing that needs to be taken into is the fact that I need new Runks created with the player ids that have not yet uploaded a Runk.
So if for group 32 player 1, 2 & 3 have already uploaded a Runk... the Runk that will need to be created needs to belong to player 4.
This is what my table looks like:

Answer 1

For the sake of an answer, here is a simplified example (apologies for the terrible naming...):
CREATE TABLE users (
user_id int,
);
INSERT INTO users (1), (2), (3);
CREATE TABLE users_list (
user_id int
);
INSERT INTO users_list values (1), (1), (1), (3);
-- SELECT as shown
SELECT user_id, count(user_id)
FROM users_list
GROUP BY user_id;
+---------+----------------+
| user_id | count(user_id) |
+---------+----------------+
| 1 | 3 |
| 3 | 1 |
+---------+----------------+
-- Incorrect, count includes all an entry even if the left join has nulls
SELECT u.user_id, count(u.user_id)
FROM users u
LEFT JOIN users_list ul ON u.user_id = ul.user_id
GROUP BY u.user_id;
# Gives - WRONG
+---------+------------------+
| user_id | count(u.user_id) |
+---------+------------------+
| 1 | 3 |
| 2 | 1 |
| 3 | 1 |
+---------+------------------+
-- Doesn't include the nulls in the count so we ge the correct answer
SELECT u.user_id, count(ul.user_id)
FROM users u
LEFT JOIN users_list ul ON u.user_id = ul.user_id
GROUP BY u.user_id;
+---------+-------------------+
| user_id | count(ul.user_id) |
+---------+-------------------+
| 2 | 0 |
| 1 | 3 |
| 3 | 1 |
+---------+-------------------+