Question

I have the following database design:

Employees Table: EmployeeID, Name, OrgCode
Departments Table: OrgCode, DepatName
CompleteSurvey Table: ID, ParticipantID

And I need to develop a table that shows the total number of employees in each department, and the total number of participants who completed the survey in each department, too. Then, I want to show the percentage of participation in each department which is mainly equal to the total number of participants / total number of employees.

I came up with the following two queries but I have to come up with one query that shows the above requirement, so how to do that?

---

Total number of employees in each department:

SELECT COUNT(DISTINCT dbo.Employees.EmployeeID) AS [Total Number of Employees], 
       dbo.Departments.DepartmentName
FROM dbo.Departments 
INNER JOIN dbo.Employees ON dbo.Departments.OrgCode = dbo.Employees.OrgCode
GROUP BY dbo.Departments.DepartmentName

---

Total number of participants in each department:

 SELECT COUNT(DISTINCT dbo.Employees.EmployeeID) AS [Total Number of Employees], 
 dbo.Departments.DepartmentName
 FROM dbo.Departments 
 INNER JOIN dbo.Employees ON dbo.Departments.OrgCode = dbo.Employees.OrgCode 
 INNER JOIN dbo.CompleteSurvey ON dbo.Employees.EmployeeID = dbo.CompleteSurvey.RespondantID
 GROUP BY dbo.Departments.DepartmentName

The problem with the second query that shows the participants, it doesn’t show all the departments even if they have no participants, it should show zeros.

UPDATE:

Basically, what I want is to have one query that shows the total number of employees in each department and the total number of participants who completed the survey in each department, and show the percentage of participation.

Answer 1

If I understood correctly that CompleteSurvey is filled with EmployeeID when employe submits a survey, this query will retrieve the info you need. You can check live test @ Sql Fiddle.

select Departments.DepatName, 
       count (Employees.EmployeeID) Employees, 
       count (CompleteSurvey.ID) Finished,
       cast (count (CompleteSurvey.ID) as float) / count (Employees.EmployeeID)
            PercentageFinished
  from Departments
 inner join Employees 
    on Departments.OrgCode = Employees.OrgCode
  left join CompleteSurvey 
    on Employees.EmployeeID = CompleteSurvey.ParticipantID
 group by Departments.DepatName

If you need all the departments, use this query:

select Departments.DepatName, 
       count (Employees.EmployeeID) Employees, 
       count (CompleteSurvey.ID) Finished,
       case when count (Employees.EmployeeID) <> 0
            then cast (count (CompleteSurvey.ID) as float) 
                     / count (Employees.EmployeeID)
            else 0
        end PercentageFinished
  from Departments
  left join Employees 
    on Departments.OrgCode = Employees.OrgCode
  left join CompleteSurvey 
    on Employees.EmployeeID = CompleteSurvey.ParticipantID
 group by Departments.DepatName

New test @ Sql Fiddle.