mysql中的select语句where条件group by ,having , order by,limit的顺序及用法

-- 语法：
SELECT select_list　　　
FROM table_name　　
[ WHERE search_condition ]　　
[ GROUP BY group_by_expression ]　　
[ HAVING search_condition ]　　
[ ORDER BY order_expression [ ASC | DESC ] ]
[limit m,n] 

-- 示例：
-- limit 0,10是从第一条开始,取10条数据
select classNo  from table_name
group by classNo
having(avg(成绩)>70)
order by classNo
limit 0,10