@Saurabh Verma​ , Delta is ACID and has a commit log, schema, etc., that's why it is different. So when you delete all data related to the partition, it will stay there as it still has a history. INSERT OVERWRITE can overwrite data only in a specified partition (but you need to specify it). The best way is to use MERGE when you have a unique id and partitions in the ON clause.

INSERT OVERWRITE TABLE part PARTITION (p1 = 'part1') VALUES(3)