The Important Roles of EXISTS Keywords in SQL
Xie Cong-ma · Computer and Information Technology · 2015
The EXISTS keywords are widely used in SQL programming, including how to determine whether a set is empty or not, how to express the semantics such as belonging to, inclusion, equivalence and so on, and how to implement the operations like intersection, except and division etc. All of these concrete methods are discussed in this paper. Furthermore, some other topics including the basic idea of solving problems, the essential steps during programming, and the points of attention are also discussed, in a way which is easy to understand and study, in this paper. Finally, using the basic knowledge of set theory, we present a set of concise and easy-to-understand methods for solving the programming problems involved the universal quantifier or the inclusion semantics, which are thought to be hard to deal with in the existing literature.