DDL/DML/DCL/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
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
关于DML，DDL，DCL的补充
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
关于DML，DDL，DCL的补充
对于DML语句，oracle不会自动提交事务，直到有一条commit或者rollback命令来处理时才会将改动反应到数据库里。而对于DDL和DCL,oracle会马上提交，也就是说一执行完这两类语句，就会反应到数据库中，还有一种情况是，前面执行的DML没有被手动提交，执行完DDL或者DCL后，oracle也会将DML对与数据的改动提交到数据库中去。
ddl是不要事务的，也就是说，操作后就不能回滚的，事务主要是针对dml语句来说的。dml语句对数据的修改需要commit才能生效，如果rollback，将回滚你的修改。如果既没有commit又没有rollback的话，这个dml处于中间状态，涉及到的lock不会释放。对于sqlplus，默认情况下，没有显示的commit，dml是不会提交的。
不过这里需要注意，如果执行了ddl语句，是会提交这个ddl语句前所有的dml语句的，这是个隐性提交。