Oracle DDL DML DCL TCL 定义

[color=red][size=medium]DDL[/size][/color]

[b]Data Definition Language[/b] (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

[color=red][size=medium]DML[/size][/color]

[b]Data Manipulation Language[/b] (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
[color=red][size=medium]DCL[/size][/color]

[b]Data Control Language[/b] (DCL) statements. Some examples:

GRANT - gives user's access privileges to database
REVOKE - withdraw access privileges given with the GRANT command

[color=red][size=medium]TCL[/size][/color]

[b]Transaction Control Language [/b](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