根据最大出现次数和用户名的最大值选择记录

Question

The following query works ok:

SELECT user.username, preference.user_id, preference.category,COUNT(*) AS occurrences 
  FROM preference inner 
  JOIN user on preference.user_id=user.userid
 where category is not null and category!=""
 GROUP BY category,user_id 
 ORDER BY occurrences DESC ;

fiddle here

I would just like

A)To get only the most popular category for each username (The one that has the max occurrences) so for the fiddle above for user1 it would be Clothing, Shoes & Accessories (3 occurrences) and for user2 Antiques (3 occurrences), all the other rows in the example apart from those two should be omitted.

B)Another query to get the second most popular category for each username

Answer 1

You can use variables to only select the 2 most popular categories per user

SELECT * FROM (
    SELECT * ,
    @rowNum := IF(@prevUserId = user_id,@rowNum+1,1) rowNum,
    @prevUserId := user_id
    FROM (
        SELECT user.username,@prevUserId,preference.user_id, category, COUNT(*) AS occurrences
        FROM preference inner JOIN user 
        on preference.user_id=user.userid
        where category is not null and category!=""
        GROUP BY category,preference.user_id
    ) t1 order by user_id, occurrences desc
) t1 WHERE rowNum <= 2

http://www.sqlfiddle.com/#!2/ba4ba7/24