I have a question what if we try to insert same data to cassandra database . Here by same i mean a set of 100 rows is already present in cassandra database say in a test column family .Again if we try to insert the same 100 rows to cassandra database i.e. rows with same rowkey , will it be inserted again ? .
It will not be duplicated, it will be overwritten unless you place the data in a different column family or keyspace, then you can duplicate it.
Docs:
The first column value in the VALUES list is the row key value to insert. List column values in the same order as the column names are listed in the INSERT list. If a row or column does not exist, it will be inserted. If it does exist, it will be updated.