COALESCE vs. ISNULL

I found a really good article that describes the differences between COALESCE and ISNULL on SQL Server. You can read this article at http://www.aspfaq.com/show.asp?id=2532 https://web.archive.org/web/20051106162859/http://www.aspfaq.com/show.asp?id=2532. The following is a summary of the article.

	COALESCE	ISNULL
ISO SQL Standard Command	Yes	No
Number of Arguments	Unlimited	2
Return value datatype	Based on all arguments	Datatype of first argument
Computed Column Nullability	Nullable	Not Nullable

A lot of situations only require two arguments, so you will have to decide which function is best for your situation. The return value’s datatype is often the deciding factor. For example:

DECLARE @SmallString NVARCHAR(3)
SET @SmallString = NULL

SELECT ISNULL(@SmallString, N'1234567') AS [ISNULL]

SELECT COALESCE(@SmallString, N'1234567') AS [COALESCE]

Results:

ISNULL
------
123

COALESCE
--------
1234567

Another factor to consider is ISNULL will perform better in certain situations. The article listed above contains more details on this.