NULLIF

Returns null if the input matches an expression, otherwise returns the input.

Sample usage

NULLIF(Discount, -1)

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)
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