下面是一些网上找的资料，自己总结到一起。
一般sql语言增删改查和alter，比较常用，oracle里面commit和revoke比较常用，这些对于我来说很迷糊，希望自己踏实下去。
Data Definition Language (DDL) statements are used to define the database structure or schema. Some examples:
Data Manipulation Language (DML) statements are used for managing data within schema objects. Some examples:
Data Control Language (DCL) statements. Some examples:
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.