SQL语句中存在量词的深入剖析和应用探讨

In-depth Analysis and Application Discussion on SQL Statement with Existential Quantifier

很多数据库的实际应用问题需要使用存在量词才能解决,而带存在量词的SQL语句是学生掌握的难点。文章系统讨论了存在量词常见的应用,通过实例指出带存在量词的SQL语句的正确书写方法,以及如何通过谓词演算将全称和蕴含量词转换为存在量词来解决实际查询问题。同时详细分析了存在量词的SQL语句的执行过程,以方便更全面地掌握其应用。

Many practical application problems of database need to be solved by using existential quantifier, with which the SQL statement is difficult to be mastered. The paper systematically discusses common application of existential quanti- fier and points out the correct writing method of SQL statement with existential quantifier by some examples. Besides, it also demonstrates how to transform universal quantifier and implication quantifier to existential quantifier by using predi- cate calculus in order to solve real problems of query. A detailed analysis of the implementation process of the SQL state- ment with the existential quantifier is finally conducted for a more comprehensive grasp of its application.