The expression to evaluate. You can use any valid expression as the
input_expression. If the two are equal, NULLIF returns null, otherwise it returns the
input_expression. You can use any valid expression as the
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:
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: