Does null values will join in update statement ?
if both tables has null values source and target table it wil consider null values and join ?
A null value will never match another null value in a simple comparison. In Teradata a NULL value is 'unknown' - how can the database know that two 'unknown' values are the same (or different).
You can say/code:
WHERE t1.col1 is NULL and t2.col1 is NULL
...but that is not comparing them directly.