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ISNULL (Transact-SQL)

  • Άρθρο

Applies to: SQL Server Azure SQL Database Azure SQL Managed Instance Azure Synapse Analytics Analytics Platform System (PDW) SQL analytics endpoint in Microsoft Fabric Warehouse in Microsoft Fabric

Replaces NULL with the specified replacement value.

Transact-SQL syntax conventions

Syntax

ISNULL ( check_expression , replacement_value )

Arguments

check_expression

The expression to be checked for NULL. check_expression can be of any type.

replacement_value

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_expression.

Return types

Returns the same type as check_expression. If a literal NULL is provided as check_expression, ISNULL returns the data type of the replacement_value. If a literal NULL is provided as check_expression and no replacement_value is provided, ISNULL returns an int.

Remarks

The value of check_expression is returned if it's not NULL. Otherwise, replacement_value is returned after it's 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.

Note

Use COALESCE to return the first non-null value.

Examples

The Transact-SQL code samples in this article use the AdventureWorks2022 or AdventureWorksDW2022 sample database, which you can download from the Microsoft SQL Server Samples and Community Projects home page.

A. Use 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 AdventureWorks2022;
GO
SELECT AVG(ISNULL(Weight, 50))
FROM Production.Product;
GO

Here's the result set.

59.79

B. Use ISNULL

The following example selects the description, discount percentage, minimum quantity, and maximum quantity for all special offers in AdventureWorks2022. If the maximum quantity for a particular special offer is NULL, the MaxQty shown in the result set is 0.00.

USE AdventureWorks2022;
GO
SELECT Description, DiscountPct, MinQty, ISNULL(MaxQty, 0.00) AS 'Max Quantity'
FROM Sales.SpecialOffer;
GO

Here's the result set.

Description DiscountPct MinQty Max Quantity
No Discount 0.00 0 0
Volume Discount 11 to 14 0.02 11 14
Volume Discount 15 to 24 0.05 15 24
Volume Discount 25 to 40 0.10 25 40
Volume Discount 41 to 60 0.15 41 60
Volume Discount over 60 0.20 61 0
Mountain-100 Clearance Sale 0.35 0 0
Sport Helmet Discount-2002 0.10 0 0
Road-650 Overstock 0.30 0 0
Mountain Tire Sale 0.50 0 0
Sport Helmet Discount-2003 0.15 0 0
LL Road Frame Sale 0.35 0 0
Touring-3000 Promotion 0.15 0 0
Touring-1000 Promotion 0.20 0 0
Half-Price Pedal Sale 0.50 0 0
Mountain-500 Silver Clearance Sale 0.40 0 0

The following example uses ISNULL to replace a NULL value for Color, with the string None.

USE AdventureWorks2022;
GO
SELECT ProductID,
    Name,
    ProductNumber,
    ISNULL(Color, 'None') AS Color
FROM Production.Product;

Here's a partial result set.

ProductID Name ProductNumber Color
1 Adjustable Race AR-5381 None
2 Bearing Ball BA-8327 None
3 BB Ball Bearing BE-2349 None
4 Headset Ball Bearings BE-2908 None
316 Blade BL-2036 None
317 LL Crankarm CA-5965 Black
318 ML Crankarm CA-6738 Black
319 HL Crankarm CA-7457 Black

C. Test for NULL in a WHERE clause

Don't 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 AdventureWorks2022;
GO
SELECT Name, Weight
FROM Production.Product
WHERE Weight IS NULL;
GO

Examples: Azure Synapse Analytics and Analytics Platform System (PDW)

D. Use 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 AdventureWorksDW

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

Here's the result set.

52.88

E. Use 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's 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. Use 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 AdventureWorksDW

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

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