Sql Server确定性的用户定义函数

本文介绍了Sql Server确定性的用户定义函数的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！

问题描述

  c创建 >。然后，SQL Server将验证它是否符合被视为确定性的标准（它会这样做，因为它不访问任何外部表或使用非确定性函数如 getdate（））。
 
 
 您可以验证它是否与 
 
  SELECT OBJECTPROPERTY（OBJECT_ID（'[dbo]。[FullNameLastFirst]'），'IsDeterministic'）
  
将模式绑定选项添加到原始代码中可以正常工作，但版本会稍微简单一些。
 （@ 100），
 @FirstName NVARCHAR（100））
 RETURNS NVARCHAR（100） 201）
 WITH SCHEMABINDING 
 AS 
 BEGIN 
 RETURN CASE 
当@IsPerson = 0 
 OR @FirstName =''THEN @LastName 
ELSE @LastName +''+ @FirstName 
 END 
 END

I have the following user-defined function:

create function [dbo].[FullNameLastFirst]
(
    @IsPerson bit,
    @LastName nvarchar(100),
    @FirstName nvarchar(100)
)
returns nvarchar(201)
as
begin
    declare @Result nvarchar(201)
    set @Result = (case when @IsPerson = 0 then @LastName else case when @FirstName = '' then @LastName else (@LastName + ' ' + @FirstName) end end)
    return @Result
end

I can't create an Index on a computed column using this function cause it's not deterministic.Someone could explain why is it not deterministic and eventually how to modify to make it deterministic?Thanks

解决方案

You just need to create it with schemabinding.

SQL Server will then verify whether or not it meets the criteria to be considered as deterministic (which it does as it doesn't access any external tables or use non deterministic functions such as getdate()).

You can verify that it worked with

SELECT OBJECTPROPERTY(OBJECT_ID('[dbo].[FullNameLastFirst]'), 'IsDeterministic')

Adding the schemabinding option to your original code works fine but a slightly simpler version would be.

CREATE FUNCTION [dbo].[FullNameLastFirst] (@IsPerson  BIT,
                                           @LastName  NVARCHAR(100),
                                           @FirstName NVARCHAR(100))
RETURNS NVARCHAR(201)
WITH SCHEMABINDING
AS
  BEGIN
      RETURN CASE
               WHEN @IsPerson = 0
                     OR @FirstName = '' THEN @LastName
               ELSE @LastName + ' ' + @FirstName
             END
  END

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