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: