如何分别查找每个组的 MAX Count 值

Question

这是我的查询

SELECT q2.item_code
     , q2.SELL_DELIVERY_AMOUNT
     , q2.count_amount
  FROM 
     ( SELECT i.item_code
            , s.SELL_DELIVERY_AMOUNT 
            , count(s.SELL_DELIVERY_AMOUNT) count_amount
         FROM sell_delivery_items s 
            , items i
        WHERE s.item_id = i.item_id
        GROUP 
           BY SELL_DELIVERY_AMOUNT
            , item_code
     ) q2
 order 
    by item_code
     , count_amount desc 

结果是

item_code   SELL_DELIVERY_AMOUNT     count_amount
0001        50                       2
0001        100                      1
0002        150                      3

我只需要显示每个 item_code 组的最高 count_amount 行。 我已经搜索了一些答案，但仍然不能适用于我的。

这就是我想要的结果

item_code   SELL_DELIVERY_AMOUNT     count_amount
0001        50                       2
0002        150                      3

我该怎么做？谢谢大家的回答。

Answer 1

我找到了解决方案。这是我的：

SELECT q3.item_code, q3.item_name, substring_index(q3.AMOUNT_LIST, ',' , 1) as most_amount_count, 
substring_index(q3.count_list,',',1) as count_time from

(SELECT q2.item_code, q2.item_name, GROUP_CONCAT(SELL_DELIVERY_AMOUNT ORDER BY q2.count_amount DESC) as AMOUNT_LIST, 
GROUP_CONCAT(q2.count_amount ORDER BY q2.count_amount desc) as count_list from

    (SELECT  i.item_code, i.ITEM_NAME, s.SELL_DELIVERY_AMOUNT , count(s.SELL_DELIVERY_AMOUNT) as count_amount
    FROM sell_delivery_items s , items i
    WHERE s.item_id = i.item_id
    GROUP BY SELL_DELIVERY_AMOUNT, item_code
    order by item_code, count_amount desc
    )  as q2

group by q2.item_code )as q3

Answer 2

这是未经测试的，因为我没有 MySQL - 但这样的东西应该可以工作：

 SELECT  q2.item_code, q2.SELL_DELIVERY_AMOUNT, q2.count_amount
 FROM 
(SELECT  i.item_code, s.SELL_DELIVERY_AMOUNT , count(s.SELL_DELIVERY_AMOUNT)     as count_amount
FROM sell_delivery_items s , items i,  @rownum := @rownum + 1 AS rank
 WHERE s.item_id = i.item_id
 GROUP BY SELL_DELIVERY_AMOUNT, item_code) as q2
 where rank = 1
order by item_code, count_amount  desc 

您需要向内部查询添加“排名”或“行号”功能，然后向外部查询添加过滤器以仅选择排名靠前的行。

这是另一个在 MySQL 中排名的例子：Ranking by Group in MySQL

Answer 3

这个呢？

SELECT  q2.item_code, q2.SELL_DELIVERY_AMOUNT, max(q2.count_amount)
FROM 
(SELECT  i.item_code, s.SELL_DELIVERY_AMOUNT , count(s.SELL_DELIVERY_AMOUNT) as count_amount
FROM sell_delivery_items s , items i
WHERE s.item_id = i.item_id
GROUP BY SELL_DELIVERY_AMOUNT, item_code) as q2
group by q2.item_code
order by count_amount  desc

在这里order by item_code, count_amount desc，您按自然顺序订购item_code，a group by 订购的。