SQL Server自定义函数(Scalarvalued Functions)

自定义函数(User-Defined Function)有两种，一种是标量UDF(Scalar-valued Functions)和表值UDF(Table-valued Functions)，前者只返回单个数据值，而后者则返回一个表。下面示例是，是属于前者，返回单个值。

SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO

CREATE FUNCTION [dbo].[udf_Rate] 
(    
     @Numerator DECIMAL(18,6),
     @Denominator DECIMAL(18,6)
)
RETURNS DECIMAL(18,6) 
AS
 BEGIN
    DECLARE @ReturnValue DECIMAL(18,6)            
    SELECT @ReturnValue=(CASE WHEN @Denominator = 0 THEN NULL WHEN @Denominator IS NULL THEN NULL  WHEN @Denominator <> 0 THEN (ISNULL(@Numerator,0) / @Denominator) END)
    RETURN @ReturnValue
 END