Sams Teach Yourself SQL in 21 Days, Fourth Edition

Summary

Join operations enable you to query multiple tables at the same time to produce useful output. Today you learned that a join combines all possible combinations of rows present in the selected tables. These new rows are then available for selection based on the information that you want. Today, we covered several different types of joins, including equi-joins, non-equi-joins, inner joins, outer joins, and self joins. Equi-joins, the most common type of join, test for equality of columns between tables. A non-equi-join, much less common, tests for inequality. An inner join combines the rows of two tables, which produces a number of new rows that equals the product of the number of rows in each table. An outer join is a method for joining ...