PostgreSQL Aggregate Functions and Group By: Get the difference between the highest and lowest salaries

Last update on February 07 2026 12:18:24 (UTC/GMT +8 hours)

8. Write a query to get the difference between the highest and lowest salaries.

Sample Solution:

Code:

-- This SQL query calculates the salary difference between the highest and lowest salaries among employees.

SELECT MAX(salary) - MIN(salary) DIFFERENCE -- Calculates the difference between the maximum and minimum salaries from the employees table and labels the result column as "DIFFERENCE"
FROM employees; -- Specifies the table from which to retrieve data, in this case, the employees table

Explanation:

The SQL query computes the salary difference between the highest and lowest salaries among employees.
The SELECT statement is used to specify the calculation of the salary difference.
MAX(salary) retrieves the highest salary from the salary column.
MIN(salary) retrieves the lowest salary from the salary column.
MAX(salary) - MIN(salary) calculates the difference between the highest and lowest salaries.
The result column is labeled as "DIFFERENCE" using the alias DIFFERENCE.
The FROM clause specifies the table from which to retrieve the data, which is the employees table in this case.

Sample table: employees

 +-------------+-------------+-------------+----------+--------------------+------------+------------+----------+----------------+------------+---------------+
| EMPLOYEE_ID | FIRST_NAME  | LAST_NAME   | EMAIL    | PHONE_NUMBER       | HIRE_DATE  | JOB_ID     | SALARY   | COMMISSION_PCT | MANAGER_ID | DEPARTMENT_ID |
+-------------+-------------+-------------+----------+--------------------+------------+------------+----------+----------------+------------+---------------+
|         100 | Steven      | King        | SKING    | 515.123.4567       | 1987-06-17 | AD_PRES    | 24000.00 |           0.00 |          0 |   		  90 |
|         101 | Neena       | Kochhar     | NKOCHHAR | 515.123.4568       | 1987-06-18 | AD_VP      | 17000.00 |           0.00 |        100 |            90 |
|         102 | Lex         | De Haan     | LDEHAAN  | 515.123.4569       | 1987-06-19 | AD_VP      | 17000.00 |           0.00 |        100 |            90 |
|         103 | Alexander   | Hunold      | AHUNOLD  | 590.423.4567       | 1987-06-20 | IT_PROG    |  9000.00 |           0.00 |        102 |            60 |
|         104 | Bruce       | Ernst       | BERNST   | 590.423.4568       | 1987-06-21 | IT_PROG    |  6000.00 |           0.00 |        103 |            60 |
|         105 | David       | Austin      | DAUSTIN  | 590.423.4569       | 1987-06-22 | IT_PROG    |  4800.00 |           0.00 |        103 |            60 |
|         106 | Valli       | Pataballa   | VPATABAL | 590.423.4560       | 1987-06-23 | IT_PROG    |  4800.00 |           0.00 |        103 |            60 |
|         107 | Diana       | Lorentz     | DLORENTZ | 590.423.5567       | 1987-06-24 | IT_PROG    |  4200.00 |           0.00 |        103 |            60 |
|         108 | Nancy       | Greenberg   | NGREENBE | 515.124.4569       | 1987-06-25 | FI_MGR     | 12000.00 |           0.00 |        101 |           100 |
..........
|         206 | William     | Gietz       | WGIETZ   | 515.123.8181       | 1987-10-01 | AC_ACCOUNT |  8300.00 |           0.00 |        205 |           110 |
+-------------+-------------+-------------+----------+--------------------+------------+------------+----------+----------------+------------+---------------+

View the table

Output:

pg_exercises=# SELECT MAX(salary) - MIN(salary) DIFFERENCE
pg_exercises-# FROM employees;
 difference
------------
   21900.00
(1 row)

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