SQL 递归查询

create   function   f_id( 
@id   int --要查询的id 
)returns   @re   table(id   int,level   int) 
as 
begin 
declare   @l   int 
set   @l=0 
insert   @re   select   id,@l 
from   表   
where   上级id=@id 
while   @@rowcount> 0 
begin 
set   @l=@l+1 
insert   @re   select   a.id,@l 
from   表   a   join   @re   b   on   a.上级id=b.id   and   b.level=@l-1 
end 
return 
end