ISNULL (Transact-SQL)

ISNULL (Transact-SQL)

 

THIS TOPIC APPLIES TO: yesSQL Server (starting with 2008)yesAzure SQL DatabaseyesAzure SQL Data Warehouse yesParallel Data Warehouse

Replaces NULL with the specified replacement value.

Topic link icon Transact-SQL Syntax Conventions

  
ISNULL ( check_expression , replacement_value )  

-- Azure SQL Data Warehouse and Parallel Data Warehouse  
ISNULL (check_expression ,replacement_value )  

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.

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.

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. replacement_value can be truncated if replacement_value is longer than check_expression.

System_CAPS_ICON_note.jpg Note


Use COALESCE (Transact-SQL) to return the first non-null value.

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 AdventureWorks2012;  
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 AdventureWorks2012. If the maximum quantity for a particular special offer is NULL, the MaxQty shown in the result set is 0.00.

USE AdventureWorks2012;  
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 AdventureWorks2012;  
GO  
SELECT Name, Weight  
FROM Production.Product  
WHERE Weight IS NULL;  
GO  

D. Using ISNULL with AVG

The following example finds the average of the weight of all products in a sample table. It substitutes the value 50 for all NULL entries in the Weight column of the Product table.

-- Uses AdventureWorks  
  
SELECT AVG(ISNULL(Weight, 50))  
FROM dbo.DimProduct;  

Here is the result set.

--------------------------   
52.88   

E. Using ISNULL

The following example uses ISNULL to test for NULL values in the column MinPaymentAmount and display the value 0.00 for those rows.

-- Uses AdventureWorks  
  
SELECT ResellerName,   
       ISNULL(MinPaymentAmount,0) AS MinimumPayment  
FROM dbo.DimReseller  
ORDER BY ResellerName;  
  

Here is a partial result set.

ResellerName MinimumPayment

------------------------- --------------

A Bicycle Association 0.0000

A Bike Store 0.0000

A Cycle Shop 0.0000

A Great Bicycle Company 0.0000

A Typical Bike Shop 200.0000

Acceptable Sales & Service 0.0000

F. Using IS NULL to test for NULL in a WHERE clause

The following example finds all products that have NULL in the Weight column. Note the space between IS and NULL.

-- Uses AdventureWorks  
  
SELECT EnglishProductName, Weight  
FROM dbo.DimProduct  
WHERE Weight IS NULL;  

Expressions (Transact-SQL)
IS NULL (Transact-SQL)
System Functions (Transact-SQL)
WHERE (Transact-SQL)
COALESCE (Transact-SQL)

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