Question

I have 2 tables.

quiz table 
=================
id, q_name, code


completed_quizes table
======================================================
id, completion_date, user_id, quiz_code, quiz_count

I have 2 types of quizes

Table_name: quiz_names
id     q_name              code
1      grand_quiz          gra
2      normal_quiz         nor

Table_name: completed_quizes
id    completion_date         user_id      q_code   q_count
1     1340841600 (28June2012)    2          gra       0
2     1340755200(27June2012)     2          nor       3
3     1340668800(26June2012)     2          nor       2
4     1340582400(25June2012)     2          nor       1
5     1340496000(24June2012)     2          gra       0
6     1340841600 (28June2012)    3          gra       0
7     1340755200(27June2012)     3          nor       3
8     1340668800(26June2012)     3          nor       2
9     1340582400(25June2012)     3          nor       1
10    1340496000(24June2012)     3          gra       0

Rules:

1- first of all all users grand quiz will be taken.

2- based on grand quiz, if any user last quiz was grand quiz then next suggestion will be normal quiz 1.

3- based on normal quiz 1 , if any user last quiz was normal quiz 1 then next suggestion will be normal quiz 2.

4- based on normal quiz 2 , if any user last quiz was normal quiz 2 then next suggestion will be normal quiz 3.

5- if any users last quiz was normal quiz 3 then again grand quiz will be next suggestion.

P.S

Problem is that every users next suggestion is based upon his previous completed quiz. I want all users who’s what will be the next quiz?

Any advice please?

Answer 1

You need the groupwise maximum to obtain the latest quiz performed by each user, then add 1 (using MOD to rotate back to 0 those who’ve most recently taken quiz 3). To include users who have not yet taken any quiz, you need to make an outer join with your user table:

SELECT user_id, IFNULL((q_count+1) % 4, 0) AS next
FROM   users LEFT JOIN (
  completed_quizes NATURAL JOIN (
    SELECT   user_id, MAX(completion_date) AS completion_date
    FROM     completed_quizes
    GROUP BY user_id
  ) AS t
) USING (user_id)

See it on sqlfiddle.