数据库中的DML，DCL，DDL分别是那些操作？

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