SQL HAVING Clause

In its most common usage, SQL HAVING clause is a SQL WHERE clause for groups. Just as SQL WHERE clause limits rows, SQL HAVING clause limits groups. In most programming contexts, you will use SQL HAVING clause after SQL GROUP BY clause to limits groups by searched conditions.

Here we have two tables

Departments

department_id  name                
-------------  --------------------
            1  Software Engineering
            2  Sale                
            3  Marketing           
            4  HR 

And Employees

employee_id  name      department_id  job_id  salary 
-----------  --------  -------------  ------  -------
          1  jack                  1       1  3000.00
          2  mary                  2       2  2500.00
          3  newcomer         (NULL)       0  2000.00
          4  anna                  1       1  2800.00
          5  Tom                   2       2  2700.00
          6  foo                   3       3  4700.00

Here we can find out which department has equal or more than 2 employees

SELECT D.name as department_name,
	   count(employee_id) AS employee_count  
FROM employees AS E 
INNER JOIN departments AS D 
	ON D.department_id = E.department_id  
GROUP BY department_name  
HAVING employee_count >= 2

and the output is
 

 department_name       employee_count
--------------------  --------------
Sale                               2
Software Engineering               2