Database management systems notes

Joins

Every kind of join, what each one does to unmatched rows, and the mistakes that quietly change your answer. Every section is a drawn page beside a clear written explanation, about 22 minutes in all.

  • Chapter 9 of 34
  • About 22 minutes
  • 8 sections
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The first drawn page of Joins: INNER JOIN: matched rows only
The chapter's first page: INNER JOIN: matched rows only

In this chapter

  • INNER JOIN: matched rows only
  • LEFT JOIN: keep everything on the left
  • FULL OUTER and CROSS joins
  • ON, USING and NATURAL
  • Self joins
  • The trap: a WHERE clause that undoes your outer join
  • The trap: row multiplication and inflated sums
  • Reading a join before you trust it

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