Returns a null value if the two specified expressions are equivalent.
NULLIF ( expression , expression )
Is a constant, column name, function, subquery, or any combination of arithmetic, bitwise, and string operators.
Returns the same type as the first expression.
NULLIF returns the first expression if the two expressions are not equivalent. If the expressions are equivalent, NULLIF returns a null value of the type of the first expression.
NULLIF is equivalent to a searched CASE function in which the two expressions are equal and the resulting expression is NULL.
This 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 as well as to include the budget value from the previous year (use the previous_year value, where the current_year is 0), combine the NULLIF and COALESCE functions.
USE pubs IF EXISTS (SELECT TABLE_NAME FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_NAME = 'budgets') DROP TABLE budgets GO SET NOCOUNT ON CREATE TABLE 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) GO SET NOCOUNT OFF SELECT AVG(NULLIF(COALESCE(current_year, previous_year), 0.00)) AS 'Average Budget' FROM budgets GO
Here is the result set:
Average Budget ---------------------------------------- 212500.000000 (1 row(s) affected)