PostgreSQL ROUND() Function Explained with Examples

Learn how to use PostgreSQL ROUND() to round numeric values to a specific number of decimal places. Includes examples for AVG(), practical SQL queries, and beginner-friendly explanations.

ROUND() is used to round a decimal number to a specific number of decimal places.

In your query:

ROUND(AVG(amount), 2)

It means:

• AVG(amount) → calculates the average payment.
• 2 → keeps 2 digits after the decimal point.
• ROUND() → rounds the result to those 2 decimal places.

Example

Suppose the average payment is:

4.356789

Using:

ROUND(4.356789, 2)

Result:

4.36

Another example:

ROUND(10.124, 2)

Result:

10.12

ROUND(10.126, 2)

Result:

10.13

In your query

SELECT
    customer_id,
    ROUND(AVG(amount), 2) AS average_payment
FROM payment
GROUP BY customer_id;

Meaning: For each customer, calculate the average payment and display it with only 2 decimal places.

Remember: ROUND(number, 2) = round the number to 2 decimal places.