sql - "Subquery returned more than 1 value"用于 SELECT 子查询

Question

我正在使用 MS SQL Server Management Studio 2008。我在编写子查询时遇到问题。这是整个查询如下:

SELECT DISTINCT 
    FH.ShipDate, AVG(FH.[Dist Freight]) AS [Atlantic Freight Charge], 
    (SELECT DISTINCT [Non-Atlantic Freight Charge]
     FROM 
         (SELECT DISTINCT 
              FH.ShipDate, AVG(FH.[Dist Freight]) AS [Non-Atlantic Freight Charge]
          FROM dbo.vw_FreightHistory AS FH
          WHERE VendorName != 'Atlantic Trucking'
          GROUP BY ShipDate, VendorName) AS [Non-Atlantic Freight Charge])
FROM dbo.vw_FreightHistory as FH
WHERE VendorName = 'Atlantic Trucking'
GROUP BY ShipDate, VendorName
ORDER BY ShipDate

问题首先出现在我添加第二个子查询时。第一个子查询没有返回任何错误，但它显示了每个 ShipDate 记录中“Dist Freight”的全部平均总和，而不是仅显示该 ShipDate 的平均值。我写了第二个子查询来尝试修复它，但现在我收到了这个错误:

Msg 512, Level 16, State 1, Line 1
Subquery returned more than 1 value. This is not permitted when the subquery follows =, !=, <, <= , >, >= or when the subquery is used as an expression.

如果我需要澄清任何事情，请告诉我。

Answer 1

我想你想要的是这样的:

 SELECT 
    FH.ShipDate, 
    AVG(CASE 
           WHEN VendorName = 'Atlantic Trucking' 
           THEN FH.[Dist Freight] 
           ELSE NULL 
        END) AS [Atlantic Freight Charge],  
    AVG(CASE 
           WHEN VendorName != 'Atlantic Trucking' 
           THEN FH.[Dist Freight] 
           ELSE NULL 
         END) AS [Non-Atlantic Freight Charge]
FROM 
    dbo.vw_FreightHistory as FH
GROUP BY 
    ShipDate
ORDER BY 
    ShipDate