SQL SUM function

Here is a clear, practical guide to the SQL SUM function, with examples, behavior notes, and best practices.

 What SQL SUM function Does

SUM() returns the total of all non-NULL numeric values in a column.

 Basic Syntax

 Basic Examples

1. Total sales amount

 SUM with WHERE (filter rows first)

 SUM with GROUP BY

Compute totals per category, per customer, etc.

 Important Behavior Notes

• SUM() ignores NULL values
•  Returns NULL if all rows are NULL
•  Works only on numeric data types
•  Often combined with GROUP BY for summary reports

 Real-World Use Cases

Monthly revenue