Number of employees for each department

July 16, 2023

I am trying to find the number of employees for each department. I have the following setup and code, which almost works.

As you can see I have 4 departments but only 3 of them (1,2,4) have employees. How can I get department 3 in my output that shows 0 employees.


CREATE TABLE departments(  department_id, department_name) AS
SELECT 1, 'IT' FROM DUAL UNION ALL
SELECT 2, 'Sales' FROM DUAL UNION ALL
SELECT 3, 'Marketing' FROM DUAL UNION ALL
SELECT 4, 'Finance' FROM DUAL;

CREATE TABLE employees (employee_id, first_name, last_name, hire_date, salary,  department_id) AS
SELECT 1, 'Lisa', 'Saladino', DATE '2001-04-03', 160000, 1 FROM DUAL UNION ALL
SELECT 2, 'Sandy', 'Herring', DATE '2011-08-04', 150200, 1 FROM DUAL UNION ALL
SELECT 3, 'Beth', 'Cooper', DATE '2019-03-05', 60700, 1 FROM DUAL UNION ALL
SELECT 4, 'Carol', 'Orr', DATE '2007-11-11', 70125,1 FROM DUAL UNION ALL
SELECT 5, 'Vicky', 'Palazzo', DATE '2004-09-17', 68525,2 FROM DUAL UNION ALL
SELECT 6, 'Cheryl', 'Ford', DATE '2020-05-10', 110000,1 FROM DUAL UNION ALL
SELECT 7, 'Leslee', 'Altman', DATE '2008-12-10', 66666, 1 FROM DUAL UNION ALL
SELECT 8, 'Jill', 'Coralnick', DATE '2001-04-11', 190000, 2 FROM DUAL UNION ALL
SELECT 9, 'Faith', 'Aaron', DATE '2001-04-17', 122000,2 FROM DUAL UNION ALL
SELECT 10, 'Silvio', 'Dante', DATE '2022-10-16', 102150,4 FROM DUAL UNION ALL
SELECT 11, 'Jerry', 'Torchiano', DATE '2022-10-30', 112660,4 FROM DUAL;

select 
  d.department_id,
  d.department_name, 
 count(*) as cnt
 from departments d
 INNER join employees e  on e.department_id = d.department_id 
 group by
   d.department_id,
   d.department_name
ORDER BY d.department_id;

Department_Id Department_name CNT
1   IT       6
2   Sales    3
4   Finance  2

>Solution :

Use a left outer join, not an inner join. And count the e.eployee_id.

select 
  d.department_id,
  d.department_name, 
 count(e.employee_id) as cnt
 from departments d
 left outer join employees e  on e.department_id = d.department_id 
 group by
   d.department_id,
   d.department_name
ORDER BY d.department_id;

See this sqlFiddle