Oracle编程高手箴言：位图索引的故事

核心提示： I have encountered issues such as this many times when an application is being moved from database A to database B. When an application that work

I have encountered issues such as this many times when an application is being moved from database A to database B. When an application that worked flawlessly in database A does not work, or works in an apparently bizarre fashion, on database B, the first thought is that database B is “bad” database. The simple truth is that database B just works differently. Neither database is wrong or “bad; they are just different. Knowing and understanding how they both work will help you immensely in dealing with these issues.

(当人们把一个应用从一种数据库迁移到另一种数据库时，他们常常抱怨同样的问题。本来这个应用程序在数据库A上运行得很好，当迁移到数据库B时，就出问题了。于是他们就认定，数据库B真烂。但事实并非如此，这只是因为数据库B的工作方式和原理不同于数据库A而已。世界上没有哪个数据库是“烂”数据库，关键是我们必须深入了解该数据库的架构和特点，这样才能避免这类问题。如果您理解位图索引的适用条件，您还会说Oracle是一个很“烂“的数据库吗？)

最后，Tom乘机建议他们，如果你们愿意，我可以给你们做一次简单的为期3天的培训。这些Java程序员听从了Tom同志的建议，经过了3天的培训后，他们对Oracle能做的事情表示吃惊，他们纷纷表示，“我真傻，原来Oracle不适合建立临时表呀，你看我的程序老是在那里删除和创建临时表。”，“要是我用了物化视图(MateralizedView)，我的数据备份代码就异常简单了。”，“我还不知道connectby有这么强大的功能呢！”。