ISNULL and COALESCE

Question

Do ISNULL and COALESCE perform the same function in SQL Server?

Jignesh Kumar · Answer

Hi Aradhana, Both ISNULL and COALESCE are used to replace NULL values. However, ISNULL only accepts two arguments, whereas COALESCE can handle two or more values and returns the first non-NULL value from the list. Examples : Suppose you're selecting a customer's contact information. You want to show the email , but if it's not available, fall back to phone , and if that’s also missing, then use 'Not Available' . -- Using COALESCE: SELECT COALESCE(Email, Phone, 'Not Available') AS PreferredContact FROM Customers; This only checks Email and directly falls back to 'Not Available' , ignoring Phone Note : So, COALESCE is more flexible when dealing with multiple fallback options. -- Using ISNULL (limited to two values): SELECT ISNULL(Email, 'Not Available') AS PreferredContact FROM Customers;

Amit Mohanty · Answer

ISNULL and COALESCE in SQL Server are similar in that both return the first non-null expression, but they differ in behavior, data type handling, and standards compliance. Both return the first non-null value and are used to handle NULLs in SQL queries. Key Differences Arguments : ISNULL takes exactly 2 arguments; COALESCE takes 2 or more. Return Type : ISNULL returns the type of the first argument; COALESCE uses data type precedence. ANSI Standard : ISNULL is not ANSI-compliant; COALESCE is ANSI-compliant. Evaluation : ISNULL evaluates expressions once; COALESCE may evaluate multiple times. Nullability : ISNULL may not preserve nullability; COALESCE better preserves nullability metadata.

Cynthia Sathuragiri · Answer

ISNULL and COALESCE both return the first non-null value, but COALESCE can take more than two values and follows data type rules more strictly. SELECT ISNULL(NULL, 'A') -- Output: 'A' SELECT COALESCE(NULL, NULL, 'B') -- Output: 'B' ISNULL is simpler but limited to two values, while COALESCE is more flexible.

ISNULL and COALESCE

Answers (3)