摘要
文章在深刻理解空值语义的基础上 ,给出了一种处理占位型空值的方法。讨论了空值环境下关系数据库的查询处理策略及程序实现 ,定义了含三种查询操作的关系代数最小完备集中的关系代数运算 。
In this paper,a method to process holdplace is proposed on the basis of the semantics of null value and the prgram design and querying policy under null value circumstances in relational database is discussed.Moreover,the fundamental operations in relational algebra with three kinds of querying operations are defined.Also,soundness and completeness in querying calculation are analysed at the end the paper.
出处
《交通与计算机》
2001年第1期47-51,共5页
Computer and Communications
基金
国家民委科研资助基金 !(982 0 0 2 )
关键词
空值环境
关系数据库
查询
程序设计
null value circumstances
relational database
query
program design
