mysql - sql中select语句中聚合函数可能的位置和执行顺序？

Question

我可以在一个 SQL 查询中的什么位置放置聚合函数(在 select 子句、having 子句或其他子句中)。聚合函数在select语句的逻辑处理顺序中的执行顺序是怎样的？

帖子“Order Of Execution of the SQL query”没有涵盖函数的执行顺序。

Answer 1

1)子查询可以放在sql语句的Where、from和中间之后。

//After Where   
 select * from orders where order_id in (select Oreder_id from OrderConfirmed)
// After From
 Select * from (select * from table) a
//Middle of sql Statement
 select id,(select Id from table1) form table2


 2) You Can put Aggregation function in both select clause and having clause.

    //In select
    select count(employee) from employees group by employee_dept
    //In having
    select count(employee) from employees group by employee_dept having(max(salary)>2000) 

3) order of execution of sql statement

  1)From 

  2)Where

  3)Group By

  4)Having

  5)aggregate Function

  6)Select