substr() 不能跟在 group by 后，求解！该怎么解决

substr() 不能跟在 group by 后，求解！
select substr(id,1,6),count(*) from tbl where (jkrq is null or jkrq<"10-1-2009") and (card not like 'a%') group by substr(id,1,6)；
报错
201: A syntax error has occurred.
Error in line 1
Near character position 124

group by id 就可以 group by substr(id,1,6) 就报错！ 求解！

------解决方案--------------------------------------------------------
group by 1 是什么意思？
以第一列