The DROP STATEMENT statement frees resources used by the named prepared statement. These resources are allocated by a successful
PREPARE statement, and are normally not freed until the database connection is released.
To drop the statement, you must first have prepared the statement.
Vendor extension. In the SQL/2008 standard, this functionality is provided by the DEALLOCATE PREPARE statement, which
is part of the optional SQL language feature B032, "Extended dynamic SQL".