Getting Started with SQL and Databases: Managing and Manipulating Data with SQL

© The Author(s), under exclusive license to APress Media, LLC, part of Springer Nature 2023

M. SimonGetting Started with SQL and Databaseshttps://doi.org/10.1007/978-1-4842-9493-2_9

9. Set Operations

Mark Simon¹  

(1)

Ivanhoe VIC, VIC, Australia

 

Behind all SQL databases is Relational Database theory, which gives databases a solid mathematical foundation. Among other things, databases are based on mathematical sets.

In mathematics, a set is a collection of things. You don’t need to worry about all of the details, but two points are important:

• A set has no duplicates. This is part of why good database design ensues that there are no repetitions.

• A set is unordered. Of course, you can’t view the contents without its being in some sort of order, but the ...