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MSDN Library

NULLIF (Transact-SQL)

Returns a null value if the two specified expressions are equal.

Applies to: SQL Server (SQL Server 2008 through current version), Azure SQL Database.

Topic link icon Transact-SQL Syntax Conventions

NULLIF ( expression , expression )


Is any valid scalar expression.

Returns the same type as the first expression.

NULLIF returns the first expression if the two expressions are not equal. If the expressions are equal, NULLIF returns a null value of the type of the first expression.

NULLIF is equivalent to a searched CASE expression in which the two expressions are equal and the resulting expression is NULL.

We recommend that you not use time-dependent functions, such as RAND(), within a NULLIF function. This could cause the function to be evaluted twice and to return different results from the two invocations.

A. Returning budget amounts that have not changed

The following example creates a budgets table to show a department (dept) its current budget (current_year) and its previous budget (previous_year). For the current year, NULL is used for departments with budgets that have not changed from the previous year, and 0 is used for budgets that have not yet been determined. To find out the average of only those departments that receive a budget and to include the budget value from the previous year (use the previous_year value, where the current_year is NULL), combine the NULLIF and COALESCE functions.

USE AdventureWorks2012;
IF OBJECT_ID ('dbo.budgets','U') IS NOT NULL
   DROP TABLE budgets;
CREATE TABLE dbo.budgets
   dept            tinyint   IDENTITY,
   current_year      decimal   NULL,
   previous_year   decimal   NULL
INSERT budgets VALUES(100000, 150000);
INSERT budgets VALUES(NULL, 300000);
INSERT budgets VALUES(0, 100000);
INSERT budgets VALUES(NULL, 150000);
INSERT budgets VALUES(300000, 250000);
   previous_year), 0.00)) AS 'Average Budget'
FROM budgets;

Here is the result set.

Average Budget



(1 row(s) affected)

B. Comparing NULLIF and CASE

To show the similarity between NULLIF and CASE, the following queries evaluate whether the values in the MakeFlag and FinishedGoodsFlag columns are the same. The first query uses NULLIF. The second query uses the CASE expression.

USE AdventureWorks2012;
SELECT ProductID, MakeFlag, FinishedGoodsFlag, 
   NULLIF(MakeFlag,FinishedGoodsFlag)AS 'Null if Equal'
FROM Production.Product
WHERE ProductID < 10;

SELECT ProductID, MakeFlag, FinishedGoodsFlag,'Null if Equal' =
       WHEN MakeFlag = FinishedGoodsFlag THEN NULL
       ELSE MakeFlag
FROM Production.Product
WHERE ProductID < 10;

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