SQL编写自定义查询

Question

I need to write a SQL Query which generates the name of the most popular story for each user (according to total reading counts). Here is some sample data:

story_name | user  | age | reading_counts
-----------|-------|-----|---------------
story 1    | user1 | 4   | 12
story 2    | user2 | 6   | 14
story 4    | user1 | 4   | 15

This is what I have so far but I don't think it's correct:

Select *
From mytable
where (story_name,reading_counts)
IN (Select id, Max(reading_counts)
      FROM mytable
      Group BY user
)

Answer 1

• In a Derived Table , you can first determine the maximum reading_counts for every user ( Group By with Max() )
• Now, simply join this result-set to the main table on user and reading_counts , to get the row corresponding to maximum reading_counts for a user.

Try the following query:

SELECT 
  t1.* 
FROM mytable AS t1 
JOIN 
(
  SELECT t2.user, 
         MAX(t2.reading_counts) AS max_count 
  FROM mytable AS t2
  GROUP BY t2.user 
) AS dt 
  ON dt.user = t1.user AND 
     dt.max_count = t1.reading_counts 

Answer 2

SELECT * 
FROM mytable
WHERE user IN
(SELECT user, max(reading_counts)
FROM mytable
GROUP BY user)