Type Ahead - How to show list from related field values "& Current Field entries"

There is more than one way to get "type ahead" to work. What method have you used?

And is this just a field formatted with a drop down list?, the filter field for a portal? or ???

The fact that the data resides in two different tables will make this a challenge.

Probably.

We would need to see how you have your type ahead feature set up.

Triggers/scripts/etc...

If filtering values listed in a portal, you might set up two portals filtered by the same text field and place those portals side by side or one above the other.

The problem is that you can't have a value list draw values from two different tables, thus this won't work. You'll need to consider other approaches--such as not allowing data to be in the local table without being also in the table on which you have based your value list. Another option might be some sort of scheduled script that regularly updates a third table with values from the other two and using that as your value list here.

And since the third table need only store unique values, you might leverage a "create" enabled relationship to do this:

If you have this relationship:

Table1::ValueField = TableOfValues::ValueField   with "allow creation" enabled for TableOfValues,

Set Field [ TableOfValues::ValueField ; Table1::ValueField ]

Will create a new record in TableOfValues if a record with a matching value does not exist, but there is no change to the table if it does.