索引是怎样提高查询的速度的，原理是什么？


举个例子:

就象你书的目录.

书的内容是数据

书的目录是索引

Oracle索引大致可分为B tree索引,Bitmap索引等索引

具体的索引可看看数据结构的书

这样说吧

索引是平衡树结构

比如你在数组查询中使用两分法查询比顺序查找快,就是这个道理

而不使用索引的表扫描就是顺序查找的

Re: 呵呵

It's very correct to say a B-Tree index is a balanced tree. But if you give an example of using a binary tree, it would be helpful to point out that the "b" in binary has nothing to do with the "B" in B-Tree, which means "Balanced" only. By the way, how many books published in China have an index at the end now? 10 years ago I worked at a publishing company in China and felt strongly we needed to encourage publishers to index all published books (maybe except dictionaries). Yong Huang 最初由 biti_rainy 发布 这样说吧 索引是平衡树结构 比如你在数组查询中使用两分法查询比顺序查找快,就是这个道理 而不使用索引的表扫描就是顺序查找的 另外索引只检索索引列。再根据 rowid 取数据。 我的理解是如果不用索引，那么检索时就是全表搜索full scanner,若用索引 ，就是在索引列的基于列的检索，可以大大降低了成本，