PostgreSQL – SUM() Function

PostgreSQL provides with a SUM() function that is used to get the addition of values of a numeric column.

Syntax: SUM(column)

The following points needs to be kept in mind while using the above function:

It ignores all NULL values.
If used with DISTINCT operator as SUM(DISTINCT column), it skips duplicate values.
Using SUM() function with SELECT clause returns NULL instead of Zero.

For examples we will be using the sample database (ie, dvdrental).

Example 1:
In this example we will calculate the total amount paid by each customer using the SUM() function and GROUP BY clause as follows:

SELECT
    customer_id,
    SUM (amount) AS total
FROM
    payment
GROUP BY
    customer_id;

Output:

Example 2:
In this example we will query for the top 10 customers who paid the most as follows:

SELECT
    customer_id,
    SUM (amount) AS total
FROM
    payment
GROUP BY
    customer_id
ORDER BY total DESC
LIMIT 10;

Output:

Article Tags :

PostgreSQL