在sqlserver里有substring()函数可以截取字符串，但是如果要截取指定的字节数，却不可以。
找了一下，发现sqlserver2005下面有个datalength()函数可以计算出字节数，于是我用这个函数写了一个SubstringEx()函数用来截取字节数。
如果哪位朋友发现已有的函数可以调用或者更好的方法，请指出。鄙人的方法实在不敢恭维，见笑了。
set ANSI_NULLS ON
set QUOTED_IDENTIFIER ON
go
-- =============================================
-- Author: sicnco
-- Create date: 2007/04/06 20:10
-- Description: substring by byte
-- =============================================
CREATE FUNCTION [dbo].[SubstringEx]
(
-- Add the parameters for the function here
@Text1 VARCHAR(255), --The string which need to be changed
@StartIndex int, --The start of position
@Offset int --The count of bytes which want to be getted
)
RETURNS varchar(255) --The string which want to be getted
AS
BEGIN
-- Declare the return variable here
declare @Index int
declare @Count1 int
declare @Len int
declare @Text2 varchar(255) --temp var string which want to be getted
set @Count1 = 0;
set @Len = len(@Text1)
set @Text2 = @Text1;
if (@Len < @StartIndex)
return @Text2
if (@StartIndex <= 0)
return @Text2
--if ((@StartIndex + @Offset - 1) > @Len)
-- return @Text2
set @Text2 = ''
set @Index = @StartIndex
while (@Index <= 255)
begin
if datalength(substring(@Text1, @Index, 1)) = 1
set @Count1 = @Count1 + 1
else
set @Count1 = @Count1 + 2
if @Count1 <= @Offset AND @Index <= @Len
begin
set @Text2 = @Text2 + substring(@Text1, @Index, 1)
set @Index = @Index + 1
continue
end
else
break
end
return @Text2
END
