How do I drop all partitions at once in hive?

alter table schema_name.table_name drop partition (partition_column != '');

You may use something similar to this:

ALTER TABLE schedule_events drop if exists partition (year>'0');

There are multiple options, here is one:

alter table schedule_events drop if exists partition (year<>'');

Hive: Extend ALTER TABLE DROP PARTITION syntax to use all comparators

"... To drop a partition from a Hive table, this works:
ALTER TABLE foo DROP PARTITION(ds = 'date')
...but it should also work to drop all partitions prior to date.
ALTER TABLE foo DROP PARTITION(ds < 'date') This task is to implement ALTER TABLE DROP PARTITION for all of the comparators, < > <= >= <> = != instead of just for ="

https://issues.apache.org/jira/browse/HIVE-2908