SQL: Visual QuickStart Guide

Creating Outer Joins with OUTER JOIN

In the preceding section, you learned that inner joins return rows only if at least one row from both tables satisfies the join condition(s). An inner join eliminates the rows that don’t match with a row from the other table, whereas an outer join returns all rows from at least one of the tables (provided that those rows meet any WHERE or HAVING search conditions).

Outer joins are useful for answering questions that involve missing quantities: authors who have written no books or classes with no enrolled students, for example. Outer joins also are helpful for creating reports in which you want to list all the rows of one table along with matching rows from another table: all authors and any books that sold ...