感覺自己是比較笨的，學習過SQL語言，但是卻分不太清楚DDL、DML、DCL語言，所以呢，今天就厚著臉皮問了老師，現在就自己目前的了解來總結一下。
1、DDL（DATA DEFINITION LANGUAGE）數據描述語言
DDL語句不會產生還原數據，所以刪除的數據也是無法恢復的
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
GRANT - gives user's Access privileges to database
REVOKE - withdraw Access privileges given with the GRANT command
2、DML（DATA MANIPULATION LANGUAGE）數據操縱魚語言
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
CALL - call a PL/SQL or Java subprogram
EXPLAIN PLAN - explain Access path to data
LOCK TABLE - control concurrency
3、DCL（DATA CONTROL LANGUAGE）數據控制語言
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 what rollback segment to use
感覺是要好那麼一點了，至少不那麼糊塗了，畢竟自己也學了那麼久，不能什麼都不知道三，不能只曉得就一個create、update、drop，嘿
