Hi @wu cong? , thank you for your question.
Do you mean you want to know which values in ColC appear in tableA but not in tableB, and vice versa?
If so, you can perform an outer join and use these columns as key columns; then, keep only the records where one of the columns is null. These will be the records where there isn't a shared value between the two tables.
I hope that makes sense; please feel free to elaborate on the ask if I didn't hit the mark.
Thanks,
Amit.