数据库中聚集索引的B树结构及实例分析

索引是数据库的对象之一，在关系数据库中，索引建立在一张基本表的一列或多列上，索引的逻辑结构是一张二维表，索引表由两类信息组成，一是索引关键字，即在基本表上经常查询的一列或多列属性，二是地址信息，即索引关键字在基本表中所在行的物理地址；索引的物理结构以B树形式组织。按照对基本表的组织方式，索引分为聚集索引和非聚集索引；按照索引关键字取值的唯一性，分为唯一索引和不唯一索引。文章着重探讨聚集索引及其B树结构，用实例分析二维表的B树索引的创建，在B树结构上的查询和更新操作，形象说明索引是如何提高查询效率的，以及进行更新操作时对索引的影响。

The B Tree Structure of Clustered Index in Database and Instance Analysis

Index is one of the objects of the database. In relational database, the index is based on one or more columns in a table. The logic structure of the index is a two-dimensional table, which is composed of two kinds of information, one is the index keywords, that is query attributes which used frequently; the second is the address information, that is physical address which indicates the storage location of the indexing key words. The Physical structure of the index is organized by B tree. According to the organized form of basic table, index can be divided into clustered index and non-clustered index. According to the uniqueness of index key values, index can be divided into the unique index and non-unique index. This paper discusses the clustered index and its B tree structure. It analyzes the creation of the B-tree by example, the query and update operations on B tree. It shows how to improve the query efficiency through index, and some influence about index when updating .