Oracle 语言分类（DDL，DML，DCL，TCL）

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 update)

　　CALL - call a PL/SQL or Java subprogram

　　EXPLAIN PLAN - explain access path to data

　　LOCK TABLE - control concurrency

DCL

　　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

　　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