IS NULL (Transact-SQL)

Makale
09/03/2024

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

Determines whether a specified expression is NULL.

Transact-SQL syntax conventions

Syntax

expression IS [ NOT ] NULL

Arguments

expression
Is any valid expression.

NOT
Specifies that the Boolean result be negated. The predicate reverses its return values, returning TRUE if the value is not NULL, and FALSE if the value is NULL.

Result Types

Boolean

Return Code Values

If the value of expression is NULL, IS NULL returns TRUE; otherwise, it returns FALSE.

If the value of expression is NULL, IS NOT NULL returns FALSE; otherwise, it returns TRUE.

Remarks

To determine whether an expression is NULL, use IS NULL or IS NOT NULL instead of comparison operators (such as = or !=). Comparison operators return UNKNOWN when either or both arguments are NULL.

Examples

The following example returns the name and the weight for all products for which either the weight is less than 10 pounds or the color is unknown, or NULL.

USE AdventureWorks2022;  
GO  
SELECT Name, Weight, Color  
FROM Production.Product  
WHERE Weight < 10.00 OR Color IS NULL  
ORDER BY Name;  
GO

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

The following example returns the full names of all employees with middle initials.

-- Uses AdventureWorks  
  
SELECT FirstName, LastName, MiddleName  
FROM DIMEmployee  
WHERE MiddleName IS NOT NULL  
ORDER BY LastName DESC;

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