Question

我的查询应该计算上个月内特定客户被添加到表中的次数。如果仅使用：

WHERE Return_Table.DateAdded >= DATEADD(month, -1, GETDATE())

然后我在上个月获得了所有的“ CustomerID”和“ TimesReturned”，这似乎是有效的，但是当我使用“ AND”和“ OR”搜索特定条目时，我得到的结果如下所示，但是结果不再计算上个月内的条目。

实际上，当我在搜索中包含或多或少的特定客户时，“ TimesReturned”值将发生变化。因此，如果我先搜索“ cust1-4”，然后搜索“ cust1-2”，TimesReturned计数将发生1和2的变化。

MyQuery：

SELECT TOP 20 Return_Table.Customer_ID, COUNT(*) AS TimesReturned
FROM Return_Table         
WHERE Return_Table.DateAdded >= DATEADD(month, -1, GETDATE()) AND
 Return_Table.Customer_ID ='cust1' OR
 Return_Table.Customer_ID ='cust2' OR
 Return_Table.Customer_ID ='cust3' OR
 Return_Table.Customer_ID ='cust4'
GROUP BY Return_Table.Customer_ID
ORDER BY TimesReturned DESC

结果：

Customer_ID TimesReturned
   Cust1         24
   Cust2         14
   Cust3         4
   Cust4         2
   .....        ....

尽管此结果的格式是正确的，但我的查询必须有问题才能使值更改为这样。

Answer 1

仔细查看WHERE子句：

WHERE Return_Table.DateAdded >= DATEADD(month, -1, GETDATE()) AND
 Return_Table.Customer_ID ='cust1' OR
 Return_Table.Customer_ID ='cust2' OR
 Return_Table.Customer_ID ='cust3' OR
 Return_Table.Customer_ID ='cust4'

它将匹配以下行：

添加的日期是过去一个月，客户id ='cust1'
客户ID ='cust2'
或客户ID ='cust3'

等等。这说明了为什么原始计数（没有客户ID过滤器）的计数增加。添加括号，您应该会很好：

WHERE
 Return_Table.DateAdded >= DATEADD(month, -1, GETDATE()) AND
 (
 Return_Table.Customer_ID ='cust1' OR
 Return_Table.Customer_ID ='cust2' OR
 Return_Table.Customer_ID ='cust3' OR
 Return_Table.Customer_ID ='cust4'
 )

PS：以上内容与以下内容相同：

WHERE
 Return_Table.DateAdded >= DATEADD(month, -1, GETDATE()) AND Return_Table.Customer_ID ='cust1' OR
 Return_Table.DateAdded >= DATEADD(month, -1, GETDATE()) AND Return_Table.Customer_ID ='cust2' OR
 Return_Table.DateAdded >= DATEADD(month, -1, GETDATE()) AND Return_Table.Customer_ID ='cust3' OR
 Return_Table.DateAdded >= DATEADD(month, -1, GETDATE()) AND Return_Table.Customer_ID ='cust4'

Answer 2

使用in运算符代替多个OR：

SELECT TOP 20 Return_Table.Customer_ID,
COUNT(*) AS TimesReturned
 FROM Return_Table         
 WHERE Return_Table.DateAdded >= DATEADD(month, -1, GETDATE()) AND
 Return_Table.Customer_ID in ('cust1' ,'cust2' 'cust3','cust4')
 GROUP BY Return_Table.Customer_ID
 ORDER BY  TimesReturned DESC

Answer 3

您需要使用括号，当您将or与多个and一起使用时，最好使用括号，否则根据运算符优先级来处理结果

 SELECT TOP 20 Return_Table.Customer_ID,
      COUNT(*) AS TimesReturned
     FROM Return_Table         
     WHERE Return_Table.DateAdded >= DATEADD(month, -1, GETDATE()) AND
     (Return_Table.Customer_ID ='cust1' OR
      Return_Table.Customer_ID ='cust2' OR
      Return_Table.Customer_ID ='cust3' OR
      Return_Table.Customer_ID ='cust4'
       )
     GROUP BY Return_Table.Customer_ID

     ORDER BY  TimesReturned DESC

SQL-使用逻辑运算符（在何处放置括号）

3 个答案: