Truncate & Drop table...

use firstkeyspace;

// Insert Data into Table
insert into firsttable(subject, mark) values('history', '70');

// Select Data
select * from firsttable;
 subject | mark
---------+------
 history |   70

(1 rows)

// Truncate table
truncate table firsttable;

cqlsh:firstkeyspace> // Select Data
cqlsh:firstkeyspace> select * from firsttable;

 subject | mark
---------+------

(0 rows)

// Drop table
cqlsh:firstkeyspace> drop table firsttable;
cqlsh:firstkeyspace> select * from firsttable;
InvalidRequest: Error from server: code=2200 [Invalid query] message="unconfigured table firsttable"