MySQL Query which require multiple joins - mysql

Question

I have a system that is used to log kids' their behavior. If a child is naughty it is logged as negative and if it has a well behaviour it is logged as positive.
For instance - if a child is rude it gets a 'Rude' negative and this is logged in the system with minus x points.
My structure can be seen in this sqlfiddle - http://sqlfiddle.com/#!9/46904
In the users_rewards_logged table, the reward_id column is a foreign key linked to either the deductions OR achievements table depending on the type of column.
If type is 1 is a deduction reward, if the type value is 2 is a achievement reward.
I basically want a query to list out something like this:
+------------------------------+
| reward | points | count |
+------------------------------+
| Good Work | 100 | 1 |
| Rude | -50 | 2 |
+------------------------------+
So it tallys up the figures and matches the reward depending on type (1 is a deduction, 2 is a achievement)
What is a good way to do this, based on the sqlfiddle?

Answer 1

Here's a query that gets the above desired results:
SELECT COALESCE(ua.name, ud.name) AS reward,
SUM(url.points) AS points, COUNT(url.logged_id) AS count
FROM users_rewards_logged url
LEFT JOIN users_deductions ud
ON ud.deduction_id = url.reward_id
AND url.type = 1
LEFT JOIN users_achievements ua
ON ua.achievement_id = url.reward_id
AND url.type = 2
GROUP BY url.reward_id, url.type
Your SQLFiddle had the order of points and type in the wrong order for the table users_rewards_logged.
Here's the fixed SQLFiddle with the result:
reward points count
Good Work 100 1
Rude -50 2

Answer 2

Although eggyal is correct--this is rather bad design for your data--what you ask can be done, but requires a UNION clause:
SELECT users_achievements.name, users_rewards_logged.points, COUNT(*)
FROM users_rewards_logged
INNER JOIN users_achievements ON users_achievements.achievement_id = users_rewards_logged.reward_id
WHERE users_rewards_logged.type = 2
UNION
SELECT users_deductions.name, users_rewards_logged.points, COUNT(*)
FROM users_rewards_logged
INNER JOIN users_deductions ON users_deductions.deduction_id = users_rewards_logged.reward_id
WHERE users_rewards_logged.type = 1
GROUP BY 1, 2
There's no reason NOT to combine the achievements and deductions tables and just use non-conflicting codes. If you combined the tables, then you would no longer need the UNION clause--your query would be MUCH simpler.

Answer 3

I noticed that you have two tables (users_deductions and users_achievements) that defines the type of reward. As #eggyal stated, you are violating the principle of orthogonal design, which causes the lack of normalization of your schema.
So, I have combined the tables users_deductions and users_achievements in one table called reward_type.
The result is in this fiddle: http://sqlfiddle.com/#!9/813d5/6