NULLIF – (Definition by Microsoft) returns NULL if the two expressions are equal and if the expressions are different then returns the first expression.

A simple representation as below:

Another way of representing

Case when Expression1 = Expression2 Then NULL Else Expression1 End

It is important to be aware that non-deterministic functions may have an impact since it evaluates two times and returns different values. Eg. NEWID(), RAND() etc.

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