在SQL Server中从字符串转换为uniqueidentifier错误时转换失败

Question

我一直收到错误"从字符串转换为uniqueidentifier时转换失败",最后我的绳子结束了.我把问题缩小到尽可能小,同时保持错误.如果要重现,请首先从此处安装CSV分割器:

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

这是测试代码.我在SQL 2008R2上,但在与SQL 2005兼容的数据库中:

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, ',')
)

这里是DelimitedSplit8K函数的源代码,因此您无需去找它:

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

使用这个UDF确实是对执行顺序的程序性假设.它假定WHERE的UDF内条款将被评估之前的cast(item as uniqueidentifier).这个假设是错误的,因为优化器可以自由地改变计划以将WHERE子句移动到转换器上方,并且净效果是要求转换器将部分令牌转换为guid(即类似字符串18E809E-EA7A-44B5-B230-776C42594D91).

有关更详细的答案,请阅读T-SQL函数并不意味着某种执行顺序.

作为一种变通方法,您可以将NULL强制为UDF的投影值,以用于不符合WHERE子句的行:

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表达式保证在CAST之前被评估(因为CAST的输入是CASE的输出),所以WHERE子句的重新排序是安全的.

Answer 2

不确定这里发生了什么,但问题似乎不是guid的格式或函数的输出.执行此工作:

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

也许查询处理器正在查看函数的返回模式并说它无法转换为uniqueidentifier？希望其他人可以提供具体的答案.

选择split函数的输出到临时表将起作用:

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
)