The NULLIF function takes two arguments. If the two arguments are equal, then NULL is returned. Otherwise, the first argument is returned. The syntax for NULLIF is as follows:

NULLIF ("expression 1", "expressions 2")

It is the same as the following CASE statement:

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


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

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