SQL NULL Functions

SQL IFNULL(), ISNULL(), COALESCE(), and NVL() Functions

Look at the following “Products” table:

Suppose that the “UnitsOnOrder” column is optional, and may contain NULL values.

Look at the following SELECT statement:

SELECT ProductName, UnitPrice * (UnitsInStock + UnitsOnOrder)
FROM Products; 

In the example above, if any of the “UnitsOnOrder” values are NULL, the result will be NULL.

Solutions

MySQL

The MySQL IFNULL() function lets you return an alternative value if an expression is NULL:

SELECT ProductName, UnitPrice * (UnitsInStock + IFNULL(UnitsOnOrder, 0))
FROM Products; 

or we can use the COALESCE() function, like this:

SELECT ProductName, UnitPrice * (UnitsInStock + COALESCE(UnitsOnOrder, 0))
FROM Products; 

SQL Server

The SQL Server ISNULL() function lets you return an alternative value when an expression is NULL:

SELECT ProductName, UnitPrice * (UnitsInStock + ISNULL(UnitsOnOrder, 0))
FROM Products; 

MS Access

The MS Access IsNull() function returns TRUE (-1) if the expression is a null value, otherwise FALSE (0):

SELECT ProductName, UnitPrice * (UnitsInStock + IIF(IsNull(UnitsOnOrder), 0, UnitsOnOrder))
FROM Products; 

Oracle

The Oracle NVL() function achieves the same result:

SELECT ProductName, UnitPrice * (UnitsInStock + NVL(UnitsOnOrder, 0))
FROM Products;