数据定义方法，创建数据表，更改数据表相关信息，新增分区等等操作
Data Definition Language (DDL) statements are used to define the database structure or schema. Some examples:
CREATE – to create objects in the database
ALTER – alters the structure of the database
DROP – delete objects from the database
TRUNCATE – remove all records from a table, including all spaces allocated for the records are removed
COMMENT – add comments to the data dictionary
RENAME – rename an object
DML
数据操纵\处理方法，主要是查询、插入等常见的数据库操作
Data Manipulation Language (DML) statements are used for managing data within schema objects. Some examples:
SELECT – retrieve data from the a database
INSERT – insert data into a table
UPDATE – updates existing data within a table
DELETE – deletes all records from a table, the space for the records remain
MERGE – UPSERT operation (insert or update)
CALL – call a PL/SQL or Java subprogram
EXPLAIN PLAN – explain access path to data
LOCK TABLE – control concurrency
DCL
数据控制方法，主要是涉及权限的事情，在 hive 中可以设置表格不被删除，仅供查询类似权限
Data Control Language (DCL) statements. Some examples:
GRANT – gives user’s access privileges to database
REVOKE – withdraw access privileges given with the GRANT command
TCL
直白的翻译就是交易控制，这些看了下面相关的理论你会发现这根数据库事务处理相关，比如涉及到回滚之类
Transaction Control (TCL) statements are used to manage the changes made by DML statements. It allows statements to be grouped together into logical transactions.
COMMIT – save work done
SAVEPOINT – identify a point in a transaction to which you can later roll back
ROLLBACK – restore database to original since the last COMMIT
SET TRANSACTION – Change transaction options like isolation level and what rollback segment to use
