SQL NULLIF Function

The NULLIF function takes two arguments. If the two arguments are equal, then NULL is returned. Otherwise, the first argument is returned.

It is the same as the following CASE statement:

SELECT CASE ("column_name")
  WHEN "expression 1 = expression 2 " THEN "NULL"
  [ELSE "expression 1"]
  END
FROM "table_name"

For example, let's say we have a table that tracks actual sales and sales goal as below:

Table Sales_Data

Store_name	Actual	Goal
Store A	50	50
Store B	40	50
Store C	25	30

We want to show NULL if actual sales is equal to sales goal, and show actual sales if the two are different. To do this, we issue the following SQL statement:

SELECT Store_name, NULLIF(Actual,Goal) FROM Sales_Data;

The result is:

Store_name	NULLIF(Actual,Goal)
Store A	NULL
Store B	40
Store C	25