在SQL查询中使用聚合函数

Question

I have my Table structure like this ::

ATT_Table : Fields - Act_ID, Assigned_To_ID, Percent_Complete(Integer value)
Act_ID is primary key, Assigned_To_ID is referenced to Emp_ID in Employee_Table.

Employee_Table : Fields - Emp_ID, F_Name. 
Emp_ID is primary key.

Now at a particular point in time, 1 or more activities can be assigned to same person. My goal is write a query to calculate a person's load. I want to count the number of activities assigned to a particular person (can be more than 1) then take the average of their percent_Complete .

For example if person A is assigned A1, A2, A3(Act_ID). Then corresponding (Percent_Complete values addition)/3. Basically an average. In my final query result I want:

Name, Number of activities assigned(Count), load value(Avg). 

How do I this? Do I have to use a nested WHERE IN clause ? Thanks.

Answer 1

SELECT  MIN(F_Name) Employee_Name ,
        COUNT(1) Activities_Assigned ,
        AVG(Percent_Complete) Load_Value
FROM    ATT_Table a
        INNER JOIN Employee_Table e ON a.Assigned_To_ID = e.Emp_ID
GROUP BY e.Emp_ID

Answer 2

我可能会遗漏一些细微差别，但听起来您可以：联接表，按员工分组， COUNT和AVG进行加载。

Answer 3

try the following:

select Emp_ID, F_Name, count(Act_ID), avg(Percent_Complete)
from ATT_Table, Employee_Table where ATT_Table.Assigned_To_ID = Employee_Table.Emp_ID
group by Emp_ID, F_Name

Answer 4

As Dmitri said, something like

SELECT Employee_Table.F_Name, COUNT(*) AS activities, AVG(Percent_Complete) AS load
FROM ATT_Table JOIN Employee_Table ON ATT_Table.Assigned_to_ID = Employee_Table.Emp_ID
WHERE Employee_Table.Emp_ID = 42
GROUP BY Employee_Table.Emp_ID