How to create a lookup subsearch with NOT IN

[ub_ik]

I am facing following challenge. I have a lookup table myids.csv with ID's in it:

ID
1
2
3

I have and index also with IDs in it (less than in the lookup):

ID
1
2

I am lookup for a way to only show the ID from the lookup that is not present in the index.

ID
3

Any suggestions?

[PickleRick · Accepted solution]

The usual - append two sets, count, find the ones that have too few occurrences.

https://www.duanewaddle.com/proving-a-negative/

[ub_ik]

perfect, thx a lot.