The ISNULL() function returns the particular value if the expression is NULL. If the expression is NOT NULL, then ISNULL() function returns the expression.

**SQL ISNULL()**

SQL ISNULL() is a built-in function used to replace the **NULL** values with the specified value. The **ISNULL( )** function is available in MySQL and SQL Server database management systems.

**SQL** Server **ISNULL**( ) function replaces the NULL value with another value. This is because NULL has been replaced by 100 via the **ISNULL()** function, so the total becomes 300 + 100 = 400.

MySQL **ISNULL( )** function tests whether the expression is **NULL**. If the expression is **NULL**, the ISNULL() function returns 1. Otherwise, this function returns 0.

**Syntax**

ISNULL(expression, value)

**Parameters**

**Expression****: It can be of any type that is used for checking NULL.****Replacement**: It returns the value type if the expression is denoted as NULL.

**Note**

**If the value of the expression evaluates to NULL, then the value of the replacement gets implicitly converted to the type of expression.**- If the expression is NOT NULL, the function returns the value of the expression.

**Query 1**

Select ISNULL (NULL, 40);

**Output**

40

**Explanation**

The function returned the second argument as the first argument specified as NULL.

**Query 2**

Select ISNULL (12, 40);

**Output**

12

**Explanation**

The function returned 1st argument, as it was NOT NULL.

**Query 3**

Select ISNULL (NULL, ‘2020-02-25’);

**Output**

‘2020-02-25’

**Explanation**

The function returned 2nd argument, as 1st argument was NULL.

**Query 4**

Select ISNULL (‘2020-02-26’, ‘2020-02-25’);

**Output**

‘2020-02-26’

**Explanation**

The function returned 1st argument, as it was NOT NULL.