使用PHP的数学，评分在1-5之间

Question

I need a rating system for my app, what happens is that a user can rate a thread 1 to 5. The calculation i was going to use was shown below:

ID        UID        TID        Rating
--------------------------------------
1         1          37         5
2         4          37         5
3         8          37         5
4         22         37         5
5         2          37         5

This is a sample table, as you can see the way i did it was,

   r1        r2        r3        r4        r5
(0 x 1) + (0 x 2) + (0 x 3) + (0 x 4) + (5 x 5)
----------------------------------------------- = 5
                    5

There is no user (UID) with a rating of 1 (r1) so you set r1 = (0 x 1) but there are users (UID) with a rating of 5 (r5) so you set r5 = (5 x 5) and the rest r2, r3, r4 are set to (0) there are no ratings for those. Hope you get it, if not ill explain more.

so i get a rating of 5 star.

But my problem is if 100 different users lets say all rate the thread 5 you will get a rating of 5 using the formula given, also if 5 different users rated another thread 5 you would get a rating of 5 also. But i don't want these results as both ratings for each thread will hit the top. I know i could select in sql to order the threads by number of users who have rated the thread so the 100 different users will go top this works, but the threads that had 5 users who rated 5 will be second.

Is there another way to rate theses threads taking into account how many users have rated each thread.

I hope you understand this, my question? if not ill edit.

I also need to generate a php script that calculates this in my select statement when i retrieve the rating, but ill ask another question when this is solved. Thanks.

Answer 1

I saw that you mentioned SELECT statements, so I assume you meant the SQL statements required.

What you asked for can be done purely using SQL itself, using the below line.

SELECT TID, AVG(RATING)  FROM ratings GROUP BY TID ORDER BY AVG(RATING) DESC, SUM(RATING) DESC;

Here is the data I used for testing.

CREATE TABLE ratings(ID INT,UID INT,TID INT,RATING INT);

INSERT INTO ratings VALUES (1,1,37,5);
INSERT INTO ratings VALUES (2,4,37,5);
INSERT INTO ratings VALUES (3,8,37,5);
INSERT INTO ratings VALUES (4,22,37,5);
INSERT INTO ratings VALUES (5,2,37,5);
INSERT INTO ratings VALUES ( 6,1,12,5);
INSERT INTO ratings VALUES ( 7,4,12,5);

SELECT TID, AVG(RATING)  FROM ratings GROUP BY TID ORDER BY AVG(RATING) DESC, SUM(RATING) DESC;

The output I got

TID AVG(RATING)
------------------
37  5
12  5