Advance filtering of select to omit values which match in another column.

[Natt_Boarer]

Scenario: I have a visitor check-in form. As a visitor checks in, I want them to be able to choose themselves from a drop-down and check in to our site. What I don't want is for them to be able to see previous check-ins.

My current select is: 

SELECT(BookInAVisitor[VisitorName],[DateArriving]>=Today())

I want to add a statement to this, which makes it an And statement, removing anyone from the list whose visitor ID is already in the column [VisitorID]

I tried using Not In This row, but it didn't work... any advice?

[Marc_Dillon]

You can use List Subtraction.

https://help.appsheet.com/en/articles/4575802-list-subtraction

[Natt_Boarer]

I had a brainwave, which works fine. Instead of subtracting, I added and ISBLANK to check if the CheckInID was complete or not, so now, it only returns future visitors who have no checkinID.