基于5VL的含空值关系数据库的选择运算

本文首先介绍了文献［1］给出的基于空值完全语义的五值逻辑（5VL），定义了基于5VL的比较运算和逻辑运算的运算规则，并以此为基础结出了一般条件表达式下选择运算的处理策略和实现算法。

In this paper, 5 valued logic (5VL) based on full semantics of null value in [1] is presented firstly, and then comparative calculation and logical calculation based on 5VL are defined. The processing policy and realizing algorithm of selecting operation under common conditional expression are given at the end of this paper.