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

Summary

We began the chapter by defining UNION and showing you the difference between linking two tables with a JOIN and combining two tables with a UNION.

We next explained how to construct a simple UNION using two SELECT statements, each of which asked for columns from a single table. We explained the significance of the ALL keyword and recommended that you use it either when you know the queries produce no duplicates or when you don’t care. We then progressed to combining two complex SELECT statements that each used a JOIN on multiple tables. Next we showed how to use UNION to combine more than two result sets. We wrapped up our discussion of UNION syntax by showing how to sort the result.

We explained how UNION is useful and listed a variety ...