create procedure p
@username varchar(30) output,
@password varchar(10) output
as
while 1>0
begin
set @username='BBS'+convert(varchar,year(getdate()))+
+convert(varchar,month(getdate()))+
+left(newid(),floor(8+rand()*4))
if not exists(select 1 from 表 where username=@username)
break;
end