關係型數據庫語言分類（DDL,DML,DCL）

關係數據庫的語言分三類，它們是（數據描述語言DDL）、（數據操縱語言DML）和（數據控制語言DCL），而SQL是（集DDL、DML、DCL爲一體）的標準關係數據庫語言。

DDL is Data Definition Language statements. 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
• GRANT - gives user's access privileges to database
• REVOKE - withdraw access privileges given with the GRANT command

DML is Data Manipulation Language statements. 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
• CALL - call a PL/SQL or Java subprogram
• EXPLAIN PLAN - explain access path to data
• LOCK TABLE - control concurrency

DCL is Data Control Language statements. Some examples:

• 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

原文引自：http://www.cnblogs.com/Shenease/archive/2008/07/15/1243365.html