Sql server SQL函数，按参数选择特定列

我有一张这样的桌子

projectID , year , jan , feb , mar , apr , may ....  

每一个代表一个数字 我想得到一个特定列上的值，它由发送给函数的值决定

我有这个功能

CREATE FUNCTION [dbo].[func_] 
(   @BRANCH_ID      NUMERIC(6,0) = 0,   
    @JOB_TYPE_ID    NUMERIC(6,0) = 0,   
    @PROJECT_ID     NUMERIC(6,0) = 0,
    @MONTH_NAME     varchar(10) = 0,    
    @YEAR_NUMBER    NUMERIC(6,0) = 0)
RETURNS NUMERIC(6,1)
AS
BEGIN
    DECLARE @FORCAST NUMERIC(6,1)

    SELECT  @FORCAST =   @MONTH_NAME
    FROM    TABLE
    WHERE   Projectid = @PROJECT_ID                                 
            AND Year = @YEAR_NUMBER

    IF @FORCAST IS NULL
        RETURN(0)

    RETURN(@FORCAST)
END

例如，如果我今天执行该函数并发送今天的年份和月份，它将在“mar”列中返回值。

如果您的SQL Server版本中提供该函数，则可以使用该函数（从SQL Server 2005开始提供）：

否则可能是这样的：

SELECT
  @FORCAST = CASE @MONTH_NAME
    WHEN 'January'  THEN jan
    WHEN 'February' THEN feb
    WHEN 'March'    THEN mar
    ...
  END
FROM [TABLE]
WHERE Projectid = @PROJECT_ID
  AND Year      = @YEAR_NUMBER

---

您能添加一些示例数据和示例函数使用情况吗？

SELECT
  @FORCAST = CASE @MONTH_NAME
    WHEN 'January'  THEN jan
    WHEN 'February' THEN feb
    WHEN 'March'    THEN mar
    ...
  END
FROM [TABLE]
WHERE Projectid = @PROJECT_ID
  AND Year      = @YEAR_NUMBER