Use NULLIF to selectively replace a specific value in your data with NULL. This can be helpful in situations where a particular value represents missing or invalid data, and you want to explicitly mark it as NULL for further analysis or processing.
Sample usage
Replace -1 in the Discount field with NULL.
Syntax
NULLIF( input_expression, expression_to_match )
Parameters
input_expression
The expression to evaluate. You can use any valid expression as the input_expression.
expression_to_match
NULLIF compares expression_to_match to input_expression. If the two are equal, NULLIF returns null, otherwise it returns the input_expression. You can use any valid expression as the expression_to_match.
Example
Suppose you want to calculate the average discount given to your customers. Your application represents "no discount" as -1. The formula AVG(Discount) will count -1 and return an incorrect result. To avoid this, you can convert those -1s to NULLS. To do this, create a new field called, for example, Discount With Nulls :
NULLIF(Discount, -1)
This formula can be read, "If the Discount field is -1, return null, otherwise return Discount."
You can then calculate the average discount ignoring orders with no discount:
AVG(Discount With Nulls)