T-SQL CASE（SQL Server 2000中）

Question

我有一个T-SQL查询，我需要从总的CASE语句计数。

我尝试添加一个UNION但我得到一个错误：

All queries in an SQL statement containing a UNION operator must have an equal number of expressions in their target lists.

任何想法？谢谢。

查询：

SELECT 
    CustomerID, Name, DueDate, 
    CASE WHEN DATEDIFF(Month, PaymentDate, DueDate) >= 1 
      THEN PaymentAmount ELSE 0 
    END AS [Early], 
    CASE WHEN DATEDIFF(Month, PaymentDate, DueDate) >=0 
      THEN PaymentAmount ELSE 0 
    END AS [On Time], 
    CASE WHEN DATEDIFF(Month, PaymentDate, DueDate) = -1 
      THEN PaymentAmount ELSE 0 
    END AS [Late] 
FROM 
    Customers 
WHERE 
    DATEDIFF(MONTH, PaymentDate,DueDate), GetDate()) = 1 
    AND PaymentAmount= DuesAmount 

UNION 

SELECT 
    '-Total', '', CustomerID, Name, DueDate, 
    SUM(CASE WHEN DATEDIFF(Month, PaymentDate, DueDate) >= 1 
       THEN PaymentAmount ELSE 0 END) AS [Early], 
    SUM(CASE WHEN DATEDIFF(Month, PaymentDate, DueDate) >= 0 
       THEN PaymentAmount ELSE 0 END) AS [On Time], 
    SUM(CASE WHEN DATEDIFF(Month, PaymentDate, DueDate) = -1 
       THEN PaymentAmount ELSE 0 END) AS [Late] 
FROM 
    Customers 
WHERE 
    DATEDIFF(MONTH, PaymentDate,DueDate), GetDate()) = 1 
    AND PaymentAmount = DuesAmount 

Answer 1

错误说，“在包含UNION操作SQL语句的所有查询必须在其目标列表中的表达式的数量相等。”这意味着每个SELECT必须返回相同数量的表达式。

在你给我们的代码示例中，第一SELECT语句返回6个表达式，而第二个返回8：

SELECT CustomerID,    -- 1 
     Name,      -- 2 
     DueDate,     -- 3 
     CASE ... END AS [Early], -- 4 
     CASE ... END AS [On Time], -- 5 
     CASE ... END AS [Late]  -- 6 
... 
UNION 
SELECT '-Total',      -- 1 
     '',        -- 2 
     CustomerID,      -- 3 
     Name,       -- 4 
     DueDate,      -- 5 
     SUM(CASE ... END) AS [Early], -- 6 
     SUM(CASE ... END) AS [On Time], -- 7 
     SUM(CASE ... END) AS [Late]  -- 8 
... 

如何看第一SELECT回报6个表达式，但第二个返回8？在UNION中，所有SELECT语句都必须返回相同数量的表达式。

您可以在第一个查询返回NULL为没有在第二匹配，如果有必要列。例如：

SELECT NULL as [RowType],   -- 1 
     NULL as [Padding],   -- 2 
     CustomerID,    -- 3 
     Name,      -- 4 
     DueDate,     -- 5 
     CASE ... END AS [Early], -- 6 
     CASE ... END AS [On Time], -- 7 
     CASE ... END AS [Late]  -- 8 
... 
UNION 
SELECT '-Total',      -- 1 
     '',        -- 2 
     CustomerID,      -- 3 
     Name,       -- 4 
     DueDate,      -- 5 
     SUM(CASE ... END) AS [Early], -- 6 
     SUM(CASE ... END) AS [On Time], -- 7 
     SUM(CASE ... END) AS [Late]  -- 8 
... 

另请注意，您在DueDate列后没有逗号。