我有一个很大的nvarchar,我希望传递给HashBytes函数.
我得到错误：
我得到错误：
“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.”
尽管如此,我发现这是由于HashBytes函数的最大限制为8000字节.进一步的搜索显示了我的一个“解决方案”,其中我的大varchar将被分开和散列,然后再结合这个用户定义的功能：
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
我打电话给：
set @ReportDefinitionHash=convert(int,dbo.[udfLargeHashTable]('SHA1',@ReportDefinitionForLookup))
@ReportDefinitionHash是int,而@ReportDefinitionForLookup是varchar
传递像’test’这样的简单的字符会产生一个与UDF不同的int,而不是HashBytes的正常调用.
关于这个问题的任何建议？
解决方法
只需使用此功能(取自
Hashing large data strings with a User Defined Function)：
create function dbo.fn_hashbytesMAX
( @string nvarchar(max),@Algo varchar(10)
)
returns varbinary(20)
as
/************************************************************
*
* Author: Brandon Galderisi
* Last modified: 15-SEP-2009 (by Denis)
* Purpose: uses the system function hashbytes as well
* as sys.fn_varbintohexstr to split an
* nvarchar(max) string and hash in 8000 byte
* chunks hashing each 8000 byte chunk,* getting the 40 byte output,streaming each
* 40 byte output into a string then hashing
* that string.
*
*************************************************************/
begin
declare @concat nvarchar(max),@NumHash int,@HASH varbinary(20)
set @NumHash = ceiling((datalength(@string)/2)/(4000.0))
/* HashBytes only supports 8000 bytes so split the string if it is larger */
if @NumHash>1
begin
-- # * 4000 character strings
;with a as (select 1 as n union all select 1) -- 2,b as (select 1 as n from a,a a1) -- 4,c as (select 1 as n from b,b b1) -- 16,d as (select 1 as n from c,c c1) -- 256,e as (select 1 as n from d,d d1) -- 65,536,f as (select 1 as n from e,e e1) -- 4,294,967,296 = 17+ TRILLION characters,factored as (select row_number() over (order by n) rn from f),factors as (select rn,(rn*4000)+1 factor from factored)
select @concat = cast((
select right(sys.fn_varbintohexstr
(
hashbytes(@Algo,substring(@string,factor - 4000,4000))
),40) + ''
from Factors
where rn <= @NumHash
for xml path('')
) as nvarchar(max))
set @HASH = dbo.fn_hashbytesMAX(@concat,@Algo)
end
else
begin
set @HASH = convert(varbinary(20),hashbytes(@Algo,@string))
end
return @HASH
end
结果如下：
select
hashbytes('sha1',N'test') --native function with nvarchar input,hashbytes('sha1','test') --native function with varchar input,dbo.fn_hashbytesMAX('test','sha1') --Galderisi's function which casts to nvarchar input,dbo.fnGetHash('sha1','test') --your function
输出：
0x87F8ED9157125FFC4DA9E06A7B8011AD80A53FE1 0xA94A8FE5CCB19BA61C4C0873D391E987982FBBD3 0x87F8ED9157125FFC4DA9E06A7B8011AD80A53FE1 0x00000000AE6DBA4E0F767D06A97038B0C24ED720662ED9F1
