Hoping there might be some thoughts on this question still.
Through some more testing, I found that by doing the following, I kind of get the result I need, but it's extremely slow, so still looking for help.
* create a new multitext field in which the Input Type is populated from a source field in the same table.
* the source (main) field is from the same table, allowing this new lookup field to now show all the values in that table for that source (main) field.
* I unchecked all the boxes under the advanced header, thinking it might help speed it up?
* on the form, I created 2 dynamic rules.
* rule 1: when record is saved and the main field has changed, change the lookup field to match this main field on the form
* rule 2: when record is saved (after checking), see if the lookup field matches the main field. Also check if the main field is not empty (since empty ones are allowed). abort with a message that the value from the main field already exists in the lookup.
This seems to work when I have the lookup field displayed on the form (which I don't want), yet it makes the form ice slow!!! basically not functional for users who don't want to wait 1-2mins. If I remove the lookup from the form, then the rules don't work it seems.
Anyways, I'm messing with that still, but hoping someone might know of a way to handle the actual question.
Thanks
