SQL NULL Functions
SQL COALESCE(), IFNULL(), ISNULL(), and NVL() Functions
Operations involving NULL values can sometimes lead to unexpected results.
SQL has some built-in functions to handle NULL values, and the most common functions are:
COALESCE()- The preferred standard. (Works in MySQL, SQL Server and Oracle)IFNULL()- (MySQL)ISNULL()- (SQL Server)NVL()- (Oracle)IsNull()- (MS Access)
Note: A NULL value represents an unknown or missing data in a database field. It is not a value itself, but a placeholder to indicate the absence of data.
Demo Database
Assume we have the following "Products" table:
| PId | ProductName | Price | InStock | InOrder |
|---|---|---|---|---|
| 1 | Jarlsberg | 10.45 | 16 | 15 |
| 2 | Mascarpone | 32.56 | 23 | null |
| 3 | Gorgonzola | 15.67 | 9 | 20 |
The "InOrder" column is optional, and may contain NULL values.
Now look at the following SQL statement:
SELECT ProductName, Price * (InStock + InOrder)
FROM Products;
Note: In the SQL above, if any of the "InOrder" values are NULL, the result will be NULL!
The COALESCE() Function
The COALESCE() function is the preferred standard for handling potential NULL values.
The COALESCE() function returns the first non-NULL value in a list
of values.
The COALESCE() function works in MySQL,
SQL Server, and Oracle (not in MS Access).
Syntax
COALESCE(val1, val2, ...., val_n)
Here we use the
COALESCE() function to replace NULL
values with 0:
SELECT ProductName, Price * (InStock + COALESCE(InOrder, 0))
FROM Products;The IFNULL() Function (MySQL)
The MySQL IFNULL()
function replaces NULL with a specified value.
Syntax
IFNULL(expr, alt)
Here we replace NULL values with 0:
SELECT ProductName, Price * (InStock + IFNULL(InOrder, 0))
FROM Products;The ISNULL() Function (SQL Server)
The SQL Server
ISNULL() function replaces NULL with a specified value.
Syntax
ISNULL(expr, alt)
Here we replace NULL values with 0:
SELECT ProductName, Price * (InStock + ISNULL(InOrder, 0))
FROM Products;The NVL() Function (Oracle)
The Oracle NVL() function replaces NULL with
a specified value.
Syntax
NVL(expr, alt)
Here we replace NULL values with 0:
SELECT ProductName, Price * (InStock + NVL(InOrder, 0))
FROM Products;The IsNull() Function (MS Access)
The MS Access
IsNull() function returns TRUE if the expression is NULL, otherwise FALSE.
Syntax
IsNull(expr)
The MS Access IIf() function returns one
of two parts, depending on the evaluation of the expression.
Syntax
IIf(expr, truepart, falsepart)
- expr - Required. The expression to evaluate
- truepart - Value to return if expr is True
- falsepart - Value to return if expr is False
Here we replace NULL values with 0:
SELECT ProductName, Price * (InStock + IIf(IsNull(InOrder), 0,
InOrder))
FROM Products;
