database joine opration

1. Joins

2. Joins
 We went over the natural join before
 There are 5 types of joins you can explicitly
state in ANSI SQL
 There are a lot of good images on the net
about this, but I’m uncomfortable with their
licensing terms, so I’m going to re-draw them
for you

3. Joining on
 Most joins require you to join “on” a particular
statement
 The statements are the same kind that are used
in WHERE clauses
 Table1.id = Table2.AddressBookId
 The PostgreSQL refers to this as the join
condition

4. Join types
 INNER JOIN
 FULL OUTER JOIN
 LEFT OUTER JOIN
 RIGHT OUTER JOIN
 CROSS JOIN

5. Inner join
 This is one of the more frequent types of joins
 Finds all rows which meet the join condition
 Example
 SELECT * FROM AddressBook a INNER JOIN
CallList c on a.id = c.addressBookId;
 a and c are aliases

6. Inner join

7. Left outer join
 Contains all records between T1 and T2 that
meet the join condition, and then any records
in T1 that don’t meet the join condition
 Rows for which the join condition is not met, the
columns of T2 are padded with nulls

8. Left outer join

9. Right outer join
 Contains all records between T1 and T2 that
meet the join condition, and then any records
in T2 that don’t meet the join condition
 Rows for which the join condition is not met, the
columns of T1 are padded with nulls

10. Right outer join

11. Full outer join
 Contains all records between T1 and T2 that
meet the join condition, and the combination
of a left outer join and right outer join are
appended onto the results

12. Full outer join

13. Implicit join notation vs. explicit
 Inner joins can be accomplished with “implicit”
join notation
 In other words, we don’t literally use the terms
“inner join” in our select statement
 We can use where clauses/multi table selects to
accomplish the same thing

14. Explicit join
 SELECT * FROM AddressBook a INNER JOIN
CallList c on a.id = c.addressBookId;

15. Implicit join
 SELECT * FROM AddressBook a, CallList c
WHERE a.id = c.addressBookId;