说明：  掌握SQL四条最基本的数据操作语句：Insert，Select，Update和Delete。 　　 练掌握SQL是数据库用户的宝贵财 富。在本文中，我们将引导你掌握四条最基本的数据操作语句—SQL的核心功能—来依次介绍比较操作符、选择断言以及三值逻辑。当你完成这些学习后，显然你已经开始算是精通SQL了。
(master four basic SQL data manipulation statement : Insert, Select, Update and Delete. Training master SQL database users is a valuable asset. In this paper, We will guide you master the four basic data manipulation statements- the core functions of the SQL-were introduced to compare operator , and three choices asserted valued logic. When you are finished learning Obviously, as you have already started a proficient SQL.)