SQL Fundamentals, Third Edition

Chapter 15. Union and Union All

The union was introduced in the last chapter because it was needed to code a full outer join. In this chapter, we discuss the union in detail. Union and union all provide two more ways to combine tables.

Forming a union can be a very powerful technique. Unfortunately, many people do not understand it or use it very well. Skillful use of unions can replace many more complex features of SQL, such as outer joins or if-then-else logic.

Union Basics		557
15-1	The difference between a union and a join	557
15-2	The difference between a union and a union all	559
15-3	The select statements within a union	561
15-4	The order by clause in a union	563
15-5	Creating a table or view that includes a union	567
15-6	Automatic datatype conversion in a ...