In Oracle11g, you can merge or split two partitions. This feature is enhanced in 12c to merge and split multiple partitions in a single SQL thus reducing the maintenance operations. When merging range partitions, they must be adjacent.
Merging Partitions Example:
ALTER TABLE SALESDATA MERGE PARTITIONS S2012Q1, S2012Q2, S2012Q3, S2012Q4 INTO S2012;
If range partitions are merged, you may use the “TO” clause.
ALTER TABLE SALESDATA MERGE PARTITIONS S2012Q1 TO S2012Q4 INTO S2012;
Read more about this feature and restrictions in Oracle Documentation.
Splitting Partitions Example:
ALTER TABLE SALESDATA SPLIT PARTITION S2014 INTO
(PARTITION S2014Q1 VALUES LESS THAN TO_DATE('01-APR-14','DD-MON-YY')),
(PARTITION S2014Q2 VALUES LESS THAN TO_DATE('01-JUL-14','DD-MON-YY')),
(PARTITION S2014Q3 VALUES LESS THAN TO_DATE('01-OCT-14','DD-MON-YY')),
(PARTITION S2014Q4 );
Read more in Oracle Documentation