Chapter 10. Complex Joins
Outer joins and self-joins are extensions of the equijoins you learned about in Chapter 7, “Equijoins.” An outer join includes the result rows returned by an equijoin, plus extra rows where no matches are found. The self-join, as implied by the name, joins a table to itself. This type of join is useful for tables with a self-referencing relationship or when you want to determine data inconsistencies. Self-joins are useful for analyzing and exploring the relationships within your data.