Question

I have a problem to express the next statement on mySql to return true results:

     select max(alltaken)mn, b.title from 
     (select  count(bc.taken) as alltaken, b.title
     from books_clients bc
     join books b on b.book_id = bc.book_id
     group by b.title) as mn
     join books b on b.title = mn.title

I need to return from the first select the count of the taken books grouped by title and in the external select to select the max number but also to display the corresponding title of the book. Written like this the statement returns the max number and the title grouped by b.title, values which are not related…

The following part of the statement returns only the max number, but I cannot transform it to return the title too 🙁 :

    select max(alltaken)mn
    (select  count(bc.taken) as alltaken, b.title
    from books_clients bc
    join books b on b.book_id = bc.book_id
    group by b.title) as mn 

Could you please help me to create the true query for my purpose.

Answer 1

You don’t even need a subquery:

SELECT COUNT(bc.taken) AS mn
     , b.title
FROM books_clients AS bc
  JOIN books b 
    ON b.book_id = bc.book_id
GROUP BY b.title
ORDER BY mn DESC
LIMIT 1

If there are more than one results with same Max count, then you need a subquery:

SELECT allb.mn
     , allb.title
FROM 
    ( SELECT COUNT(bc.taken) AS mn
      FROM books_clients AS bc
        JOIN books b 
          ON b.book_id = bc.book_id
      GROUP BY b.title
      ORDER BY mn DESC
      LIMIT 1
    ) AS maxb
  JOIN
    ( SELECT COUNT(bc.taken) AS mn
           , b.title
      FROM books_clients AS bc
        JOIN books b 
          ON b.book_id = bc.book_id
      GROUP BY b.title
    ) AS allb
    ON allb.mn = maxb.man