Using ISNULL() function

The ISNULL() function is used to return the defined input value in case the passed-in expression has NULL as its value. It only accepts two parameters and only evaluates the passed-in expression. We will walk through a few simple examples of it and do a comparison between ISNULL() and COALESCE() in this section.

How to use ISNULL()

Let’s jump into the examples!

Run the following code in SSMS:

SELECT ISNULL('Hello', 'World') AS [Output]

The result returned is as follows:

Figure 4.14 – Result of the query

As we can see, when we pass in two VARCHAR values, the function evaluates the first one (in this case, Hello) and determines it is not a NULL value, so it returns the Hello value itself as result.

Now, run the following chunk of code:

SELECT ISNULL(NULL, 'World') AS [Output]

The result we get this time is as follows:

Figure 4.15 –...