关系模式设计的规范化与非规范化

Normalization and Abnormalization of Relation Scheme Design

关系模式的规范化设计存在表的数量多、连接运算复杂、数据库执行速度慢等缺点;非规范化设计减少了查询操作所需的连接,减少了外部键和索引的数量,可以预先进行统计计算,提高了查询时的响应速度;用实例说明设计关系数据库时应根据属性数量、属性间的函数依赖、关系中元组的数量和应用来确定应采用的方法。

There are some disadvantages in normalization design such as too many tables, complex join and slow executive speed. While abnormalization design reduces joins which query requires and the number of keys and indices, can count in advance and improve the query speed. Which one is used should be decided by the number of attributes, functional dependencies, the number of tuples and applications.