@Override
	public void free_result() throws SQLException {
		// no need to close a stmt which doesn't exist
		if(this.stmt != null && !this.stmt.isClosed()) {
			this.stmt.close();
			this.stmt = null;
			this.last_prepare = "";
		}
		if(this.res != null && !this.res.isClosed()) {
			this.res.close();
			this.res = null;
		}
	}