Conversion failed when converting from a character string to uniqueidentifier error in SQL Server

Question

I\'ve been getting the error \"Conversion failed when converting from a character string to uniqueidentifier\" and am finally at the end of my rope. I\'ve narrowed down my p

Answer 1

The use of this UDF is indeed making procedural assumptions about order of execution. It assumes that the WHERE clause inside the UDF will be evaluated before the cast(item as uniqueidentifier). This assumption is erroneous as the optimizer is free to change the plan to move the WHERE clause above the cast and the net effect is that the cast is asked to converts a partial token to a guid (ie. a string like 18E809E-EA7A-44B5-B230-776C42594D91).

For a more detailed answer read T-SQL functions do no imply a certain order of execution.

As a workaround you can force NULL into the projected values of the UDF for the rows that don't meet the WHERE clause:

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

Because the CASE expression is guaranteed to be evaluated before the CAST (since the input of the CAST is the output of the CASE) the reordering of the WHERE clause is safe.

Answer 2

Why cast Item to uniqueidentifier when you can do it the other way around.

Instead of

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

you may try this:

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

Answer 3

Not sure what is happening here, but the problem does not appear to be the format of the guids or the output of the function. Executing this works:

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

Maybe the query processor is looking at the return schema of the function and saying that it can't be cast to uniqueidentifier? Hopefully someone else can provide a specific answer to that.

Selecting the output of the split function into a temp table will work:

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 4

Looks like I misread the question the first time. Good job producing a test script that reproduces the error. The following works for me:

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)