sql中的select語句中可能的位置和執行有關聚合函數的順序？

Question

在哪裏可以將聚合函數放在一個SQL查詢中（select子句中，having子句或其他）。在select語句的邏輯處理順序中，聚合函數的執行順序是什麼？

該帖子「Order Of Execution of the SQL query」沒有涵蓋功能的執行順序。

Answer 1

1）你可以在sql語句的where，from和middle之後放置子查詢。

//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