含有空值关系数据库的查询处理

本文在深刻理解空值语义的基础上，给出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策略，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，并对查询计算的有效性和完备性进行了分析。

In this paper,a method of processing holdplace is proposed on the basis of the semantics of null value. The querying policy under null value circumstances in relational database is discussed. The fundamental operations in relational algebra with three kinds of querying operations are defined. Soundness and completeness in querying calculation are analysed at the end of the paper.

国家自然科学基金