Question

Basically I need to create output TOP table where users are arranged by comparing their points with admin’s points.
For example:

User3 | 0 //Everything was as admin had.
User5 | 3 //One song had 2 points different from admin and one was off by one
ect.

In my database I have three tables:

Table: rating

+------------+---------+----------+---------+ 
| rating_id  | user_id | song_id  | points  | 
+------------+---------+----------+---------+ 
| 1          | 1       | 4        | 0       | 
| 2          | 1       | 3        | 1       | 
| 3          | 3       | 2        | 3       | 
| 4          | 4       | 2        | 2       | 
| 5          | 2       | 1        | 4       |


Table: songs

+---------------+------------+ 
| song_name_id  | song_name  | 
+---------------+------------+ 
| 1             | Song1      | 
| 2             | Song2      | 
| 3             | Song3      | 
| 4             | Song4      | 
| 5             | Song5      | 

Table: users

+----------+----------+----------+
| id       | username | password |
+----------+----------+----------+
| 1        | User1    | passw    |
| 2        | User2    | wordp    |
| 3        | User3    | somet    |
| 4        | User4    | hings    |

It should be something like this (not in any programming language):

Compare user_id > 1 with user_id=1 //Let's say that the comparable admin is user_id=1
$result= ABS(user.points-admin.points)++;

And put this to array as:

username => result

Then when I sort this array by result, I can print it as top table – who got the closest result to admin!

I tryed several different solutions but never got the right result.

Can anybody help me?

UPDATE:

Thanks!

With JOIN the result is:

+------------+---------+----------+---------+-----------+
| song_id    |song_name| user_id  |username |rating_diff|
+------------+---------+----------+---------+-----------+ 
| 1          | Song1   | 1        | admin   | 0         | 
| 2          | Song2   | 1        | admin   | 0         |
...etc...

With LEFT JOIN the result is:

+------------+---------+----------+---------+-----------+
| song_id    |song_name| user_id  |username |rating_diff|
+------------+---------+----------+---------+-----------+ 
| 1          | Song1   | 11       | user2   | NULL      | 
| 1          | Song1   | 10       | user1   | NULL      |
| 1          | Song1   | 12       | user3   | NULL      |
| 1          | Song1   | 1        | admin   | 0         |
| 2          | Song2   | 11       | user2   | NULL      | 
| 2          | Song2   | 10       | user1   | NULL      |
| 2          | Song2   | 12       | user3   | NULL      |
| 2          | Song2   | 1        | admin   | 0         |

..etc..

So.. Something is wrong, the rating_diff does not work.

Answer 1

Assuming you want this comparison on a song-by-song basis (instead of a total or average across all songs), try:

select r.song_id,
       s.song_name,
       r.user_id,
       u.username,
       abs(r.points - r1.points) rating_diff
from rating r
join songs s on r.song_id = s.song_name_id
join users u on r.user_id = u.id
join rating r1 on r.song_id = r1.song_id and r1.user_id = 1
order by s.song_name, abs(r.points - r1.points)

This should sort the output by the song name, and then by the difference between the admin’s points and the users’ points. (Change the join on rating r1 to be a left join if you can’t guarantee an admin rating for every song.)