在sql中查找开发人员的平均年龄

Question

I have the following tables in sql :

I want to find average age of Developers . I also want to find the numbers of task for each priority of a task . How can I do that ?

Answer 1

To find the average age of the developers assigned to all the tasks you need to run this query -

select AVG(e.Age) as age from `Employee` e join `Task_Assignment` ta on ta.Developer_ID = e.Employee_ID;

To find the number of tasks for each priority you need to run this query -

select COUNT(t.TASK_ID) from `Task` t join `Task_Priority` tp on t.Task_ID = tp.Task_ID GROUP_BY tp.Priority_ID;

Hope this helps :)

Answer 2

select sum(age)/count(*) as avg_age from (
select distinct developer, age from (
select * from Employee emp inner join Task_Assignment task_assign 
on emp.emp_id = task_assign.developer
) as a ) as b