To empty a table, use the TRUNCATE command.
When the truncated rows are no longer visible to any concurrent
transaction, the TRUNCATE command frees all the disk space that is
allocated to the table, making the space available for reuse.
MYDB.SCHEMA(USER)=> TRUNCATE TABLE weather;
Note: Starting in release 188.8.131.52, this command does not
require exclusive access to the table before it runs. SELECT queries
in other transactions can run concurrently with the TRUNCATE operation.
The queries in concurrent transactions see the table and its contents
from the timeframe relative to when that concurrent transaction started.