执行顺序

from -> on -> join -> where -> group by -> agg_func -> with rollup/cube -> having -> select -> distinct -> order by -> limit

having与where的区别

where是在group by 之前对表进行行级过滤。
having是在group by 之后，对group by后的结果进行过滤。

• 如找到平均工资超过20000万的员工

  select emp_no,avg(salary) as salary_avg
  from salaries
  group by emp_no
  having salary_avg > 120000
  order by salary_avg
  limit 5;