1.DDL数据定义语言（Data Definiton Language）用于create 和alter Schema。
2.DML数据操作语言（Data manipulation Language）用于操作和获取数据,insertion,update,deletion,,,,.
sql书
sql tuning,anintroduction to database system
http://www.mathcomp.uokufa.edu.iq/staff/kbs/file/2/An%20Introduction%20to%20Database%20Systems,%208th%20Edition,%20C%20J%20Date_4.pdf
原文：http://www.cnblogs.com/Donie/p/3746731.html