How to Use COALESCE in SQL: A Practical Guide

Learn when and how to use the SQL COALESCE function with examples

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Introduction

Data in real-world databases is often messy and incomplete. The COALESCE expression is a powerful SQL function that can handle null values in multiple scenarios. It is a standard SQL function and is widely supported across different database systems.

Using COALESCE can make your queries more robust and readable. In this article, you will learn:

• What is the COALESCE expression and what it returns;
• How to use the COALESCE expression and the basic syntax;
• When to use the COALESCE expression with four practical scenarios and accompanying examples;
• What are differences between COALESCE versus ISNULL in SQL.

What is COALESCE?

In SQL, the COALESCE expression can take multiple expressions of any type. It evaluates the arguments in order from left to right, and returns the data of the value with the highest precedence.

When working with null values, COALESCE will return the first non-null value in this list of expressions. If all arguments are null, then it returns null.