Why oracle does not support multiple partitions selection?

Assuming the table is partitioned weekly basis, the following SQL cannot be executed:

select * from MyTable partition (21JulyWeek1,JulyWeek2,21JulyWeek3);

Error: ORA-00933: SQL command not properly ended

To overcome this; a union-all view can be used, but it is not easy to manage.

Any idea please how to select multiple partitions/sub-partitions in Oracle 12c.

Best Regards

Ahmed