MAX和Count之间的替代

Question

我希望得到作者所写书籍的最大数量与每位作者所写的数量之间的差异。

SELECT  count(book_name) contar, (MAX(C.qty) - count(book_name)) final
FROM (select B.author_id, count(book_name) qty 
     FROM author A ,BOOK B 
     WHERE A.author_id = B.author_id 
     GROUP BY b.author_id) C , 
author A, 
BOOK B 
WHERE A.author_id = B.author_id 
    AND B.author_id=C.Author_id
    AND date_release BETWEEN NOW() - INTERVAL 20 YEAR AND NOW()
GROUP BY c.author_id
HAVING contar > 0

如您所见，有两个表BOOK包含book_id，author_id，book_name，date_release和表AUTHOR {{1 }}，author_id，author_name，author_lastname。

我收到了这个结果

但我需要像

这样的东西

date_birth

Answer 1

问题是每个作者正在计算MAX(C.qty)，因为查询有GROUP BY c.author_id。您需要为整个子查询计算此总计一次。

由于作者ID位于AUTHOR，因此在获取每位作者的图书数时，也无需加入BOOK。

SELECT  count(book_name) contar, (max_qty - count(book_name)) final
FROM (SELECT MAX(qty) AS max_qty
      FROM (select count(book_name) qty 
            FROM BOOK B 
            GROUP BY b.author_id) t
     ) C 
CROSS JOIN author A
JOIN book B ON A.author_id = B.author_id 
WHERE date_release BETWEEN NOW() - INTERVAL 20 YEAR AND NOW()
GROUP BY A.author_id

并且不需要HAVING contar > 0，因为没有书籍的作者将不会包含在JOIN中。

Answer 2

试试这个。我将每个数字等于一个变量，然后减去这些变量。然而，变量将作为列出现。

SELECT  count(book_name) contar, 
        @max:=( MAX(C.qty) ), 
        @bookcount:=( count(book_name) ), 
        @final:= @max-@bookcount
FROM (select B.author_id, 
             count(book_name) qty 
      FROM author A , BOOK B 
      WHERE A.author_id = B.author_id 
      GROUP BY b.author_id) C , 
      author A, 
      BOOK B 
WHERE A.author_id = B.author_id 
  AND B.author_id = C.Author_id 
  AND date_release BETWEEN NOW() - INTERVAL 20 YEAR 
                       AND NOW()
GROUP BY c.author_id
HAVING contar > 0