在SQL Server中将字符串转换为uniqueidentifier错误时转换失败

Question

我收到错误“从字符串转换为uniqueidentifier时发生转换失败”，并且终于出现在我的绳索末端。我将问题缩小到尽可能小，同时保持错误的机智。如果要复制从这里首先安装CSV分流：

http://www.sqlservercentral.com/articles/Tally+Table/72993/

这里的测试代码。我对SQL 2008 R2，但在数据库是SQL 2005兼容：

IF EXISTS (SELECT * FROM sys.objects WHERE object_id = OBJECT_ID(N'[dbo].[ZZZTESTTABLE]') AND type in (N'U')) 
DROP TABLE [dbo].[ZZZTESTTABLE] 
GO 

CREATE TABLE [dbo].[ZZZTESTTABLE](
    [Col1] [uniqueidentifier] NOT NULL, 
CONSTRAINT [PK_ZZZTESTTABLE] PRIMARY KEY CLUSTERED 
(
    [Col1] ASC 
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY] 
) ON [PRIMARY] 

-- Test table that I would like to check my values against 
insert dbo.ZZZTESTTABLE(Col1) values('85B049B7-CDD0-4995-B582-5A74523039C0') 

-- Test string that will be split into table in the DelimitedSplit8k function 
declare @temp varchar(max) = '918E809E-EA7A-44B5-B230-776C42594D91,6F8DBB54-5159-4C22-9B0A-7842464360A5' 

-- I'm trying to delete all data in the ZZZTESTTABLE that is not in my string but I get the error 
delete dbo.ZZZTESTTABLE 
where Col1 not in 
(
-- ERROR OCCURS HERE 
    select cast(Item as uniqueidentifier) from dbo.DelimitedSplit8K(@temp, ',') 
) 

这里的DelimitedSplit8K函数的源，所以你不必去寻找它：

CREATE FUNCTION dbo.DelimitedSplit8K 
--===== Define I/O parameters 
     (@pString VARCHAR(8000), @pDelimiter CHAR(1)) 
RETURNS TABLE WITH SCHEMABINDING AS 
RETURN 
--===== "Inline" CTE Driven "Tally Table" produces values from 0 up to 10,000... 
    -- enough to cover VARCHAR(8000) 
    WITH E1(N) AS (
       SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL 
       SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL 
       SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 
       ),       --10E+1 or 10 rows 
     E2(N) AS (SELECT 1 FROM E1 a, E1 b), --10E+2 or 100 rows 
     E4(N) AS (SELECT 1 FROM E2 a, E2 b), --10E+4 or 10,000 rows max 
cteTally(N) AS (--==== This provides the "zero base" and limits the number of rows right up front 
        -- for both a performance gain and prevention of accidental "overruns" 
       SELECT 0 UNION ALL 
       SELECT TOP (DATALENGTH(ISNULL(@pString,1))) ROW_NUMBER() OVER (ORDER BY (SELECT NULL)) FROM E4 
       ), 
cteStart(N1) AS (--==== This returns N+1 (starting position of each "element" just once for each delimiter) 
       SELECT t.N+1 
        FROM cteTally t 
        WHERE (SUBSTRING(@pString,t.N,1) = @pDelimiter OR t.N = 0) 
       ) 
--===== Do the actual split. The ISNULL/NULLIF combo handles the length for the final element when no delimiter is found. 
SELECT ItemNumber = ROW_NUMBER() OVER(ORDER BY s.N1), 
     Item  = SUBSTRING(@pString,s.N1,ISNULL(NULLIF(CHARINDEX(@pDelimiter,@pString,s.N1),0)-s.N1,8000)) 
    FROM cteStart s 
; 

Answer 1

不知道发生了什么在这里，但问题似乎并没有成为的GUID的格式或的输出功能。执行此作品：

declare @temp varchar(max) = '918E809E-EA7A-44B5-B230-776C42594D91,6F8DBB54-5159-4C22-9B0A-7842464360A5'  
select cast(Item as uniqueidentifier) from dbo.DelimitedSplit8K(@temp, ',') 

也许查询处理器看函数的返回模式和说，它不能被转换为uniqueidentifier？希望别人能够提供具体的答案。

选择拆分函数的输出到一个临时表将工作：

select cast(Item as uniqueidentifier) as Item into #temp from dbo.DelimitedSplit8K(@temp, ',') 

-- I'm trying to delete all data in the ZZZTESTTABLE that is not in my string but I get the error 
delete dbo.ZZZTESTTABLE 
where Col1 not in 
(
-- ERROR OCCURS HERE 
    --select cast(Item as uniqueidentifier) from dbo.DelimitedSplit8K(@temp, ',') 
    select Item from #temp 
) 

Answer 2

外貌就像我第一次误解了这个问题。做好产生重现错误的测试脚本。以下作品适用于我：

delete dbo.ZZZTESTTABLE 
WHERE Col1 in 
(
    select Z.Col1 
    from dbo.ZZZTESTTABLE Z 
    LEFT JOIN dbo.DelimitedSplit8K(@temp, ',') S on S.Item = Z.Col1 
    where S.Item is null 
) 
OPTION (force order) 

Answer 3

为什么投射Item到uniqueidentifier时，您可以通过其他方式做到这一点。

而不是

where Col1 not in 
(
-- ERROR OCCURS HERE 
    select cast(Item as uniqueidentifier) from dbo.DelimitedSplit8K(@temp, ',') 
) 

你可以试试这个：

where cast(Col1 as varchar(64)) not in 
(
    select Item 
    from dbo.DelimitedSplit8K(@temp, ',') 
) 

Answer 4

使用该UDF的确实是作出有关执行顺序程序的假设。它假定在​​UDF内的WHERE子句将在,cast(item as uniqueidentifier)之前被评估为。这个假设是错误的，因为优化器可以自由地更改将演算WHERE子句移动到演员上方的计划，并且净效果是要求演员将部分令牌转换为guid（即像18E809E-EA7A-44B5-B230-776C42594D91这样的字符串）。

如需更详细的解答，请阅读T-SQL functions do no imply a certain order of execution。

作为一种变通方法，您可以强制NULL到UDF的使用行的预测值不符合WHERE子句：

CREATE FUNCTION dbo.DelimitedSplit8K 
... 
cteStart(N1, nullify) AS (--==== This returns N+1 (starting position of each "element" just once for each delimiter) 
       SELECT t.N+1, 
        case when (SUBSTRING(@pString,t.N,1) = @pDelimiter OR t.N = 0) then 1 else 0 end 
        FROM cteTally t 
        WHERE (SUBSTRING(@pString,t.N,1) = @pDelimiter OR t.N = 0) 
       ) 
--===== Do the actual split. The ISNULL/NULLIF combo handles the length for the final element when no delimiter is found. 
SELECT ItemNumber = ROW_NUMBER() OVER(ORDER BY s.N1), 
     Item  = case s.nullify 
      when 1 then SUBSTRING(@pString,s.N1,ISNULL(NULLIF(CHARINDEX(@pDelimiter,@pString,s.N1),0)-s.N1,8000)) 
      else null 
      end 
    FROM cteStart s; 
go 

因为CASE表达式是保证科协之前评估（由于CAST的输入是CASE的输出）因此WHERE子句的重新排序是安全的。