DROP TABLE [IF EXISTS] [db_name.]table_name
EXTERNAL 表，请删除该表并从文件系统中删除与该表关联的目录。Drop a table and delete the directory associated with the table from the file system if this is not an
EXTERNAL table. 如果要删除的表不存在，则会引发异常。If the table to drop does not exist, an exception is thrown.
如果该表不存在，则不会执行任何操作。If the table does not exist, nothing happens.