SQL列表格

Question

是否可以为计算列规范或公式添加SELECT查询？我想使用这个查询：

SELECT IIF( [Name] = 'Tuition'
           , CONVERT([DECIMAL](15,2),Cost * t1.SubjectUnit)
           , CONVERT([DECIMAL](15,2),Cost)
       ) as FinalCost 
FROM [HCCDB].[dbo].[SubjectOfferedFee] AS t0
        INNER JOIN HCCDB.dbo.SubjectsOffered  AS t1
            ON t1.SubjectsOfferedID = t0.SubjectsOfferedID

在ALTER表语句中：

ALTER TABLE HCCDB.dbo.SubjectOfferedFee
  ADD FinalCost AS [THE QUERY SELECT QUERY ABOVE]

我在另一列上尝试过此操作，方法是通过创建新列并添加公式来连接列。

CONVERT([varchar](50),[FirstName]) 
    + ' ' + CONVERT([varchar](50),[MiddleName]) 
    + ' ' + CONVERT([varchar](4),[LastName])

它有效，但如何添加SELECT查询？

Answer 1

只需在当前上下文中创建用户定义函数。

CREATE FUNCTION dbo.fnGetSubjectCost(@id INT)
RETURNS DECIMAL 
AS 
-- Returns cost if the subject that if particular name is equal to Tuition then cost x unit.
BEGIN
DECLARE @ret DECIMAL;

SELECT @ret = IIF([Name] = 'Tuition', CONVERT([DECIMAL](15,2),Cost * t1.SubjectUnit), CONVERT([DECIMAL](15,2),Cost))
    FROM [HCCDB].[dbo].[SubjectOfferedFee] AS t0
        INNER JOIN HCCDB.dbo.SubjectsOffered  AS t1
            ON t1.SubjectsOfferedID = t0.SubjectsOfferedID
            WHERE t0.SubjectOfferedFeeID = @id
IF (@ret IS NULL) 
SET @ret = 0;
RETURN @ret;
END;
GO

然后您可以使用此函数计算列规范或

ALTER TABLE HCCDB.dbo.SubjectOfferedFee
ADD FinalCost AS CONVERT(DECIMAL(15,2), dbo.fnGetSubjectCost(CONVERT(INT, [SubjectOfferedFeeID])))

然后解决了。