When to use In/Not in Results instead of adding the Data Extension to my Selected Data Extensions?

sometimes you might want to filter using data from a data extension that you do not want to add to your selected data extensions let's see an example to understand why this could be the case suppose you have an orders data extension and a customers data extension with the records shown below true 330,331left 2 unhandled content type left unhandled content type left unhandled content type left unhandled content type left unhandled content type left unhandled content type left unhandled content type left unhandled content type left unhandled content type true 330,331left 2 unhandled content type left unhandled content type left unhandled content type left unhandled content type left unhandled content type left unhandled content type left unhandled content type because the customerid column in the orders data extension is not unique when you try to join those two data extensions, the result would look like this true 220,220,221left 3 unhandled content type left unhandled content type left unhandled content type left unhandled content type left unhandled content type left unhandled content type left unhandled content type left unhandled content type left unhandled content type left unhandled content type left unhandled content type left unhandled content type left unhandled content type because there is a one to many relationship between those two tables duplicate values on the email column show up depending on the use case, the email duplicate values that show up might be unwanted to avoid such a scenario it is recommended, when possible, to use in/not in results filter instead of adding to your selected data extensions to sum up true 330,331left unhandled content type left unhandled content type left unhandled content type left unhandled content type