Coalesce SQL

What does the COALESCE function do in SQL?

The COALESCE function returns the first non-NULL expression in a list. It's useful for handling missing or null data in queries.

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Description

Example H2

Example H3

The COALESCE function is a powerful tool in SQL for handling NULL values. It allows you to specify a list of expressions and returns the first non-NULL value from that list. If all expressions are NULL, it returns the last expression in the list. This is particularly helpful when dealing with data that might be missing or incomplete. For instance, in a customer database, a customer's phone number might be missing. Using COALESCE, you can provide a default value for the phone number if it's NULL, preventing errors or unexpected results in your queries. COALESCE is also useful for simplifying queries that need to handle different possible outcomes. Instead of writing multiple `CASE` statements or `IF` conditions, you can use COALESCE to concisely return the appropriate value.

Why Coalesce SQL is important

COALESCE is crucial for robust data handling in SQL. It prevents errors caused by NULL values and allows for more predictable query results. It simplifies code and improves readability by providing a concise way to handle missing data.

Coalesce SQL Example Usage


-- Sample table
CREATE TABLE Customers (
    CustomerID INT PRIMARY KEY,
    FirstName VARCHAR(50),
    LastName VARCHAR(50),
    Phone VARCHAR(20)
);

INSERT INTO Customers (CustomerID, FirstName, LastName, Phone)
VALUES
(1, 'John', 'Doe', '555-1212'),
(2, 'Jane', 'Smith', NULL),
(3, 'Peter', 'Jones', '555-3456');

-- Using COALESCE to handle NULL phone numbers
SELECT
    CustomerID,
    FirstName,
    LastName,
    COALESCE(Phone, 'Not Available') AS PhoneNumber
FROM
    Customers;

Coalesce SQL Syntax

Common Mistakes

Forgetting to specify a default value when using COALESCE, leading to NULL results if all values are NULL.
Using COALESCE inappropriately when a `CASE` statement or other conditional logic would be more suitable for complex scenarios.

Frequently Asked Questions (FAQs)

When should I use COALESCE instead of writing multiple CASE statements?

Use COALESCE whenever your main goal is to return the first non-NULL value from a list of columns or expressions. It condenses what might otherwise require several nested CASE statements into a single, readable function call—making queries shorter, easier to maintain, and often faster for the database to execute.

What does COALESCE return if every expression in the list is NULL?

If every expression passed to COALESCE evaluates to NULL, the function returns the last expression in the list. Because that last expression is also NULL in this scenario, the final result will be NULL—allowing you to handle complete data absence in a controlled way.

How can Galaxy’s AI SQL editor improve my workflow when using COALESCE?

Galaxy’s context-aware AI copilot auto-completes COALESCE syntax, suggests default values based on column metadata, and flags potential NULL pitfalls before you run the query. This speeds up writing COALESCE-heavy statements, reduces human error, and lets teams share endorsed, NULL-safe queries without pasting SQL back and forth in Slack or Notion.