从 GROUP BY 中获取 MAX

Posted 2023-02-24

【中文标题】从 GROUP BY 中获取 MAX

【英文标题】：Get MAX from a GROUP BY

【发布时间】：2013-01-03 01:21:28

【问题描述】：

当我遇到这种情况时，我正在练习一些 SQL。我想看看某种商品出现了多少次，然后从那里得到出现最多的商品。

这显示了每种商品出现了多少次：

mysql> SELECT commodity, COUNT(commodity) count FROM orders GROUP BY commodity ORDER BY count;
+----------------------+------------+
| commodity            |    count   |
+----------------------+------------+
| PERSIAN MELON        |          4 |
| BEANS                |          6 |
| CASABA               |         10 |
| ASPARAGUS            |         11 |
| EGGPLANT             |         12 |
| TOMATOES, CHERRY     |         16 |
| GALIA MELON          |         18 |
+-----------------------------------+

我试图获得最高的那一行，但它完全错了：

mysql> SELECT commodity, MAX(COUNT(commodity)) count FROM orders GROUP BY commodity ORDER BY count;

这样做的正确方法是什么？

【参考方案1】：

注意：查询不会处理具有最大COUNT 的重复记录

SELECT  commodity,  COUNT(commodity) `count` 
FROM    orders 
GROUP   BY commodity
ORDER   BY `count` DESC 
LIMIT   1

但这会，

SELECT  commodity,  COUNT(commodity) `count` 
FROM    orders 
GROUP   BY commodity
HAVING  COUNT(commodity) =
(
    SELECT MAX(`COUNT`) 
    FROM
    (
        SELECT  COUNT(commodity) `count` 
        FROM    orders 
        GROUP   BY commodity
    )   s
)

【讨论】：

@enchance 是的，第一个但第二个不会。考虑这条记录TOMATOES, CHERRY | 18，GALIA MELON | 18，PERSIAN MELON | 10

第一个将只显示TOMATOES, CHERRY | 18，但第二个将同时显示TOMATOES, CHERRY | 18 和GALIA MELON | 18

是的，因为它使用LIMIT 1，所以只返回最高记录。有什么方法可以解决这个问题而不必使用子查询？

【参考方案2】：

试试这个查询

  SELECT commodity,COUNT(commodity) AS count 
    FROM orders
GROUP BY commodity
ORDER BY count desc
   LIMIT 1;

【讨论】：

MAX(COUNT(commodity)) 无效！

【参考方案3】：

我会写：

select * from (SELECT commodity, COUNT(commodity) count FROM orders GROUP BY commodity ORDER BY count desc) where rownum <2;

【参考方案4】：

只要添加 desc 就可以了

SELECT commodity, COUNT(commodity) count FROM orders GROUP BY commodity ORDER BY count DESC;

第一行将具有最大值并添加限制以获取仅此一条记录

SELECT commodity, COUNT(commodity) count FROM orders GROUP BY commodity ORDER BY count DESC LIMIT 1;

【参考方案5】：

看起来你做得对。除了ORDER BY 以ASC 的顺序订购它们。让它下降

mysql> SELECT commodity, COUNT(commodity) count FROM orders GROUP BY commodity ORDER BY count DESC;

【讨论】：

MAX(COUNT(commodity)) 无效！