If both tables have the same student ID's in fields with the same data type, they should match if you link them in a relationship by the ID fields.
It is not clear what you mean by this:
Each record could have duplicate IDs but are unique from each other.
I think that you mean that this table could log multiple incidents involving the same student. If so, then the fact that you have multiple records with the same Student ID should not keep all of the record in this table with the same ID from linking to the table of IDs and Grade levels.
But if you mean that you have a student ID field with multiple student ID's entered into the same field, that might or might not cause a problem.
Is this what you have? In which table? How are the multiple ID's entered into the same field? (what character(s) separates one ID from the next?)
Thank you Phil for answering.
I have the former set-up, students may have multiple incidences that use the same Student ID. I originally did not think it would impact the "merge" but something is stopping this from working, so that was my only diagnosis.
I checked to be sure the field type was the same, it was.
I tried to set it up with a portal. It still didn't work.
I tried to make a calculation, but I'm not sure what I need to use as a calculation to make it exactly equal to a related field.
I don't know why the simple import match won't work. That would be the easiest thing to use.
You shouldn't need any calculation.
But I'm not fully clear on exactly what you are trying to do.
Do you mean that you have a grade level field in this table which you want to update with the student's grade level by doing an import with the "Match found set" option?
I would think that you would want to import this as a separate table and link it to the current table in a relationship by ID instead of copying the same grade level to multiple fields. (And there are many useful ways to use such a Students table where you have just one record for each student.)
Your import matching may fail due to the reasons you describe, I suspect that only the first matching record can be updated but this is not something that I have tested. The other way this type of import frequently fails is when the record in the target table is not part of the found set before the records are imported. In most cases, you'd want to do a show all records just before the import.