Handling NULL values effectively is crucial for maintaining data integrity. SQL Server’s COALESCE function addresses this by returning the first non-NULL value in a list.
Using coalesce
Replacing NULL values, convert NULL to placeholders for cleaner data.
SELECT Id, COALESCE(Address, 'N/A') AS Address
FROM Employee;
Sorting with defaults, use COALESCE to assign meaningful sort orders.
SELECT Id, COALESCE(Discount, 0) AS Discount
FROM Product ORDER BY Discount;
Handling math operations, prevent NULL from breaking calculations.
SELECT Price * (1 - COALESCE(Discount, 0)/100) AS FinalPrice
FROM Product;
FAQ
What does COALESCE do?
It returns the first non-NULL value from provided arguments.
Is COALESCE supported universally?
Yes, it’s ANSI-compliant, working in major databases like MySQL and PostgreSQL.
How does COALESCE differ from ISNULL?
ISNULL is SQL Server-specific, while COALESCE is part of the SQL standard.
Can COALESCE impact performance?
Yes, minimize arguments and place likely non-NULL values first for better performance.
Conclusion
SQL Server’s COALESCE ensures effective handling of NULL values in your queries. Dive deeper into its capabilities in the article A Complete Guide to the SQL Server COALESCE Function.