Syntax:
DROP TABLESPACE tablespace_name
    ENGINE [=] engine_name

This statement drops a tablespace that was previously created using
CREATE TABLESPACE (see [HELP CREATE TABLESPACE]).

*Important*:

The tablespace to be dropped must not contain any data files; in other
words, before you can drop a tablespace, you must first drop each of
its data files using ALTER TABLESPACE ... DROP DATAFILE (see [HELP
ALTER TABLESPACE]).

The ENGINE clause (required) specifies the storage engine used by the
tablespace. Currently, the only accepted values for engine_name are NDB
and NDBCLUSTER.

DROP TABLESPACE is useful only with Disk Data storage for MySQL
Cluster. See
http://dev.mysql.com/doc/refman/5.5/en/mysql-cluster-disk-data.html.

URL: http://dev.mysql.com/doc/refman/5.5/en/drop-tablespace.html

