Data warehouses commonly keep a time window of data. For example, three years of historical data is stored.
Partitioning makes it very easy to purge data from a table. You can use the DROP PARTITION or TRUNCATE PARTITION statements to purge data. Common strategies also include using a partition exchange load to unload the data from the table and replacing the partition with an empty table before dropping the partition. Archive the separate table you exchanged before emptying or dropping it.
A drop or truncate operation would invalidate a global index or a global partitioned index. Local indexes remain valid. The local index partition is dropped when you drop the table partition.
The following example shows how to drop partition sales_1995 from the sales table:
ALTER TABLE sales DROP PARTITION sales_1995 UPDATE GLOBAL INDEXES PARALLEL;