SUM() in PostgreSQL

The SUM() function in PostgreSQL calculates the total sum of a numeric column.

Syntax

SELECT SUM(column_name) FROM table_name WHERE condition;

1. Summing All Values in a Column

SELECT SUM(salary) FROM employees;

✅ Returns the total salary of all employees.

2. Using SUM() with a WHERE Condition

SELECT SUM(salary) FROM employees WHERE department = 'IT';

✅ Returns the total salary of employees in the IT department.

3. Using SUM() with GROUP BY

SELECT department, SUM(salary) FROM employees GROUP BY department;

✅ Returns the total salary for each department.

4. Using SUM() with ROUND()

SELECT ROUND(SUM(salary), 2) FROM employees;

✅ Returns the total salary rounded to 2 decimal places.

5. Handling NULL Values in SUM()

• SUM() ignores NULL values in calculations.
• If all values are NULL, it returns NULL.

Example:

SELECT SUM(bonus) FROM employees;

✅ If some employees don’t have a bonus (NULL), they are not included in the sum.