ISNULL (Transact-SQL)
Replaces NULL with the specified replacement value.
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Syntax
ISNULL ( check_expression ,replacement_value )
Arguments
check_expression
Is the expression to be checked for NULL. check_expression can be of any type.replacement_value
Is the expression to be returned if check_expression is NULL. replacement_value must be of a type that is implicitly convertible to the type of check_expresssion.
Return Types
Returns the same type as check_expression. If a literal NULL is provided as check_expression, returns the datatype of the replacement_value. If a literal NULL is provided as check_expression and no replacement_value is provided, returns an int.
Remarks
The value of check_expression is returned if it is not NULL; otherwise, replacement_value is returned after it is implicitly converted to the type of check_expression, if the types are different.
Examples
A. Using ISNULL with AVG
The following example finds the average of the weight of all products. It substitutes the value 50 for all NULL entries in the Weight column of the Product table.
USE AdventureWorks2008R2;
GO
SELECT AVG(ISNULL(Weight, 50))
FROM Production.Product;
GO
Here is the result set.
--------------------------
59.79
(1 row(s) affected)
B. Using ISNULL
The following example selects the description, discount percentage, minimum quantity, and maximum quantity for all special offers in AdventureWorks2008R2. If the maximum quantity for a particular special offer is NULL, the MaxQty shown in the result set is 0.00.
USE AdventureWorks2008R2;
GO
SELECT Description, DiscountPct, MinQty, ISNULL(MaxQty, 0.00) AS 'Max Quantity'
FROM Sales.SpecialOffer;
GO
Here is the result set.
Description DiscountPct MinQty Max Quantity
--------------- ------------- -------- ---------------
No Discount 0.00 0 0
Volume Discount 0.02 11 14
Volume Discount 0.05 15 4
Volume Discount 0.10 25 0
Volume Discount 0.15 41 0
Volume Discount 0.20 61 0
Mountain-100 Cl 0.35 0 0
Sport Helmet Di 0.10 0 0
Road-650 Overst 0.30 0 0
Mountain Tire S 0.50 0 0
Sport Helmet Di 0.15 0 0
LL Road Frame S 0.35 0 0
Touring-3000 Pr 0.15 0 0
Touring-1000 Pr 0.20 0 0
Half-Price Peda 0.50 0 0
Mountain-500 Si 0.40 0 0
(16 row(s) affected)
C. Testing for NULL in a WHERE clause
Do not use ISNULL to find NULL values. Use IS NULL instead. The following example finds all products that have NULL in the weight column. Note the space between IS and NULL.
USE AdventureWorks2008R2;
GO
SELECT Name, Weight
FROM Production.Product
WHERE Weight IS NULL;
GO