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 Oracle的语言分四类，它们是（数据定义语言DDL）、（数据操纵语言DML）、（数据控制语言DCL） 和 (事务控制语言TCL)

DDL

　　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

　　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