I want to create a validation which will allow unique row of first name, last name and email. When I enter a new row, it should not allow if the same values already exist in previous rows.

First Name Last Name Email
John Doe johndoe@email.com
Scott Doe johndoe@email.com - should be allowed
John Doe johndoe@email.com - should not be allowed
Robin Scott johndoe@email.com - should be allowed.


How do I achieve this. Thank you.