SQL Queries for Mere Mortals: A Hands-On Guide to Data Manipulation in SQL, Second Edition

SQL Set Operations

Now that you have a basic understanding of set operations, let’s look briefly at how they’re implemented in SQL.

Classic Set Operations versus SQL

As noted earlier, not many commercial database systems yet support set intersection (INTERSECT) or set difference (EXCEPT) directly. The current SQL Standard, however, clearly defines how these operations should be implemented. We think that these set operations are important enough to at least warrant an overview of the syntax.

As promised, we’ll show you alternative ways to solve an intersection or difference problem in later chapters using JOINs. Because most database systems do support UNION, Chapter 10 is devoted to its use. The remainder of this chapter gives you an overview ...