The HAVING clause is used with aggregate functions as the WHERE clause can not be used with them.

HAVING Syntax

SELECT column_name, aggregate_function(column_name)
FROM table_name
WHERE column_name operator value
GROUP BY column_name
HAVING aggregate_function(column_name) operator value;

We have a table "employee" as below:

    employee
    id  first_name            last_name       salary
    .......................................................
    1   John                     Simp         10000
    2   Chris                    Hely         25000
    3   John                     Roy          20000
    4   Jenny                    Mill         35000
    5   Jenny                    Simpson      35000

HAVING Example

Now we want to find all the records which have duplicate values in column "first_name" then you just need to write the below command:

SELECT first_name, COUNT(first_name) as count 
FROM employee
GROUP by first_name 
HAVING COUNT(first_name) > 1;

Result:

    first_name            count
    .............................
    John                  2
    Jenny                 2

Now we want to find the records which have duplicate values in column "first_name" and salary is 35000, then you just need to write the below command:

SELECT first_name, COUNT(first_name) as count 
FROM employee
WHERE salary = 35000
GROUP by first_name 
HAVING COUNT(first_name) > 1;

Result:

    first_name            count
    .............................
    Jenny                  2

Hope this will help you :)