SQL 如何查找某个字符串第N次出现的位置

if exists(select 1 from sysobjects where name='char_index')
drop function char_index

create function char_index(@string varchar(8000),@char varchar(10),@index smallint)
--@string:待查找字符串，@index:查找位置
returns smallint
as
begin
declare
@i tinyint,--当前找到第@i个
@position tinyint--所在位置
set @position=1;
set @i=0;
while charindex(@char,@string,@position)>0
begin
set @position=charindex(@char,@string,@position)+1;
set @i=@i+1;
if @i=@index
begin
return @position-1;
end
end
return 0;--0表示未找到
end

select dbo.char_index('sdf_dsf_dfgdg_ertr_erte','f_',2)

http://blog.csdn.net/zhou968/article/details/2760871