SQL NULL Functions
SQL IFNULL(), ISNULL(), COALESCE(), and NVL() Functions
Look at the following "Products" table:
| P_Id | ProductName | UnitPrice | UnitsInStock | UnitsOnOrder |
|---|---|---|---|---|
| 1 | Jarlsberg | 10.45 | 16 | 15 |
| 2 | Mascarpone | 32.56 | 23 | |
| 3 | Gorgonzola | 15.67 | 9 | 20 |
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 Productsor we can use the COALESCE() function, like this:
SELECT ProductName, UnitPrice * (UnitsInStock + COALESCE(UnitsOnOrder, 0))
FROM ProductsSQL 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 ProductsMS 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 ProductsOracle
The Oracle NVL() function achieves the same result:
SELECT ProductName, UnitPrice * (UnitsInStock + NVL(UnitsOnOrder, 0))
FROM Products
