hash - SQL Server 2008 and HashBytes

Question

I have quite a large nvarchar which I wish to pass to the HashBytes function. I get the error:

"String or binary would be truncated. Cannot insert the value NULL into column 'colname', tbale 'table'; column does not allow nulls. UPDATE fails. The statement has been terminated."

Being ever resourceful, I discovered this was due to the HashBytes function having a maximum limit of 8000 bytes. Further searching showed me a 'solution' where my large varchar would be divided and hashed seperately and then later combined with this user defined function:

function [dbo].[udfLargeHashTable] (@algorithm nvarchar(4), @InputDataString varchar(MAX))
RETURNS varbinary(MAX)
AS
BEGIN
DECLARE
    @Index int,
    @InputDataLength int,
    @ReturnSum varbinary(max),
    @InputData varbinary(max)

SET @ReturnSum = 0
SET @Index = 1
SET @InputData = convert(binary,@InputDataString)
SET @InputDataLength = DATALENGTH(@InputData)

WHILE @Index <= @InputDataLength
BEGIN
    SET @ReturnSum = @ReturnSum + HASHBYTES(@algorithm, SUBSTRING(@InputData, @Index, 8000))
    SET @Index = @Index + 8000
END
RETURN @ReturnSum
END

which I call with:

set @ReportDefinitionHash=convert(int,dbo.[udfLargeHashTable]('SHA1',@ReportDefinitionForLookup))

Where @ReportDefinitionHash is int, and @ReportDefinitionForLookup is the varchar

Passing a simple char like 'test' produces a different int with my UDF than a normal call to HashBytes would produce.

Any advice on this issue?

Answer 1

If you can't create a function and have to use something that already exists in the DB:

sys.fn_repl_hash_binary

can be made to work using the syntax:

sys.fn_repl_hash_binary(cast('some really long string' as varbinary(max)))

Taken from: http://www.sqlnotes.info/2012/01/16/generate-md5-value-from-big-data/