SQL 显示计数中的第一个和最后一个值答案

【问题标题】：SQL show the first and last value in countSQL 显示计数中的第一个和最后一个值
【发布时间】：2019-09-19 13:54:12
【问题描述】：

我需要编写一个查询来显示客户订单的最大和最小订单数。

我试过了：

(SELECT TOP 1 CustomerID, COUNT(*) AS Number_Of_Orders
FROM Orders
GROUP BY CustomerID
ORDER BY COUNT(*) ASC)

UNION ALL

(SELECT TOP 1 CustomerID, COUNT(*) AS Number_Of_Orders
FROM Orders
GROUP BY CustomerID
ORDER BY COUNT(*) DESC)

但我没有成功合并输出，我收到错误Incorrect syntax near the keyword 'ORDER'。

我怎样才能得到它？

【问题讨论】：

标签： sql sql-server tsql aggregate-functions northwind

【解决方案1】：

我不确定是否要运行两次聚合，所以使用窗口函数：

SELECT CustomerID, Number_Of_Orders
FROM (SELECT CustomerID, COUNT(*) AS Number_Of_Orders,
             ROW_NUMBER() OVER (ORDER BY COUNT(*) ASC) as seqnum_asc,
             ROW_NUMBER() OVER (ORDER BY COUNT(*) DESC) as seqnum_desc
      FROM Orders
      GROUP BY CustomerID
     ) c
WHERE seqnum_asc = 1 OR seqnum_desc = 1;

【讨论】：

【解决方案2】：

您不能在要与UNION 统一的查询中使用ORDER BY，但可以这样做：

SELECT * FROM
  (SELECT TOP 1 CustomerID, COUNT(*) AS Number_Of_Orders
  FROM Orders
  GROUP BY CustomerID
  ORDER BY COUNT(*) ASC) t
UNION ALL
SELECT * FROM
  (SELECT TOP 1 CustomerID, COUNT(*) AS Number_Of_Orders
  FROM Orders
  GROUP BY CustomerID
  ORDER BY COUNT(*) DESC) t

虽然效率低下，但这样做可以解决问题，因为您执行两次相同的代码并排序两次。

【讨论】：

【解决方案3】：

您可以为此使用窗口函数。如果有平局，这将为您提供多个客户的最小/最大数量 (fiddle)：

SELECT CustomerID
     , OrderCount
     , CASE WHEN OrderCount = MinOrderCount THEN 'Customer with min orders'
            WHEN OrderCount = MaxOrderCount THEN 'Customer with max orders' END AS Type
FROM (
    SELECT CustomerID
         , COUNT(*) AS OrderCount
         , MIN(COUNT(*)) OVER () AS MinOrderCount
         , MAX(COUNT(*)) OVER () AS MaxOrderCount
    FROM Orders
    GROUP BY CustomerID
) AS x
WHERE OrderCount = MinOrderCount OR OrderCount = MaxOrderCount

【讨论】：