将 mysql 数据库中的用户输入与 php 进行比较

Question

I have a table that stores user choices to lots of questions.
Choices are A,B or C. ( or 0,1,2 but limited to 3 same values for every question) So the table looks like this:

question user choice
1        1    A
1        2    A
1        3    B
2        1    C
2        2    A
2        3    B
3        1    B
3        2    C
3        3    B
.        .    .
.        .    .
.        .    .
N        N    N

What i want to do is to compare choices and group users with same choices like last.fm neighbours.

I can compare one user against another user with IN and NOT IN queries, or selecting all rows and comparing with php's array functions. But as the database grows this approach will not be feasible and this also compares only two users.

Maybe hashing user's choices in a way that i couldn't imagine can help.

Answer 1

SELECT a.user, b.user, COUNT(*) AS common
FROM Choice a
LEFT JOIN Choice b 
       ON a.user != b.user 
      AND a.question = b.question 
      AND a.choice = b.choice 
GROUB BY a.user, b.user

Will return for two users how many questions they have answered the same way. Maybe this helps.