Database Programming

Sections 4 – Joins

Marge Hohly 2

Overview Oracle Proprietary

Joins (8i and prior): Cartesian Product Equijoin Non-equijoin Outer join Self join

SQL: 1999 Compliant Joins: Cross joins Natural joins Using clause Full or two sided

outer joins Arbitrary join

conditions for outer joins

Marge Hohly 3

Cross Join

ANSI/ISO SQL: 1999 syntax for achieving of a Cartesian product

Syntax: SELECT *

FROM employeesCROSS JOIN departments;

Last week:SELECT *FROM employees, departments;

Marge Hohly 4

Natural Join ANSI/ISO SQL: 1999 Join equivalent of an

equijoin Join on all common columns

ie. columns with same name and data type

SYNTAX:SELECT field1, field2FROM table1 NATURAL JOIN table2WHERE fieldn = value;

Marge Hohly 5

Example 4.2.3 SELECT event_id,

song_id, cd_numberFROM d_play_list_items NATURAL JOIN d_track_listingsWHERE event_id = 105;

Marge Hohly 6

Example Natural Join

SELECT employee_id, last_name, department_id, location_idFROM employeesNATURAL JOIN departments;

Marge Hohly 7

4.2.6.5

5. Use an equijoin between the DJs on Demand database tables, d_songs and d_types. Display the type code, description and title. Limit the rows returned to those type codes between 70 and 80.

Marge Hohly 8

Join Using ANSI/ISO SQL: 1999 join condition used to

join two tables on only one column Typically used where NATURAL JOIN cannot

be used because there are other common columns with same name and different data types

No table name or alias can be used on the referenced column anywhere in the statement

Marge Hohly 9

Join Using SYNTAX:

SELECT field1, field2, field3FROM table1JOIN table2USING(column name);

Example:SELECT e.employee_id, e.last_name, d.location_idFROM employees eJOIN departments dUSING(department_id);

Marge Hohly 10

Example SELECT e.employee_id,

e.last_name, d.location_idFROM employees e JOIN departments dUSING(department_id);

Marge Hohly 11

JOIN ON ANSI/ISO: 1999 join clause that may be used to specify the

condition or columns used: Syntax:

SELECT field1, field2, field3FROM table1 JOIN table2ON(table1.fieldx=table2.fieldy);

SELECT e.last_name emp, m.last_name mgrFROM employees e JOIN employees mON(e.manager_id = m.employee_id);

SELECT e.last_name as "EMP", w.last_name as "MGR“FROM employees e JOIN employees wON (e.manager_id = w.employee_id)WHERE e.last_name like 'H%';

Where clause can limit results.

Marge Hohly 12

Example of JOIN ON SELECT e.last_name,

e.department_id, d.department_nameFROM employees e JOIN departments dON (e.department_id = d.department_id);

Marge Hohly 13

Summary/Comparison

Marge Hohly 14

Examples 4.3.6-82. Join DJs on Demand d_play_list_items, d_track_listings,

and d_cds tables with the JOIN USING syntax. Include the song ID, CD number, title, and comments in the output.

3. Display the city, department name, location ID, and department ID for departments 10, 20, and 30 for the city of Seattle.

6. Display job title, employee first name, last name, and email for all employees that are stock clerks.

9. (Use Join On) Query and display manager ID, department ID, department name, first name, and last name for all employees in departments 80, 90, 110, and 190.

Marge Hohly 15

Three-way Joins with the ON clause

A three-way join is the join of three tables Syntax:

SELECT employee_id, city, department_nameFROM employees eJOIN departments dON (d.department_id = e.department_id)JOIN locations lON (d.location_id=l.location_id);

Marge Hohly 16

Example SELECT employee_id, city,

department_nameFROM employees eJOIN departments dON (d.department_id = e.department_id)JOIN locations lON (d.location_id=l.location_id);

Marge Hohly 17

Revised example SELECT e.employee_id,

l.city, d.department_nameFROM employees e, departments d, locations lWHERE e.department_id = d.department_idAND d.location_id = l.location_id

Marge Hohly 18

INNER JOINS

An inner join returns only those rows that match the join condition

SELECT e.last_name, e.department_id, d.department_nameFROM employees eJOIN departments dON (e.department_id = d.department_id);

Marge Hohly 19

OUTER JOIN

Outer joins return those rows that match the join condition and those that do not

There are three ANSI/ISO SQL: 1999 outer joins:

LEFT OUTER JOIN RIGHT OUTER JOIN FULL OUTER JOIN

Marge Hohly 20

LEFT OUTER JOIN SELECT e.last_name, e.department_id, d.department_name

FROM employees eLEFT OUTER JOIN departments dON(e.department_id=d.department_id);

SQL 99 equivalent:

SELECT e.last_name, e.department_id, d.department_nameFROM employees e, departments dWHERE e.department_id=d.department_id(+);

This statement will return those employees who do not have a department_id

Marge Hohly 21

RIGHT OUTER JOIN SELECT field1, field2 ....

FROM table1 aRIGHT OUTER JOIN table2 bON (a.field=b.field);

or USING(field name);

SELECT e.last_name, e.department_id, d.department_nameFROM employees eRIGHT OUTER JOIN departments dON(e.department_id=d.department_id);

This statement will return those departments who do not have any employees in them

Marge Hohly 22

FULL OUTER JOIN The FULL OUTER JOIN returns both matched and all

unmatched rows Syntax:

SELECT field1, field2, field3FROM table1 aFULL OUTER JOIN table2 bON a.field=b.field;

SELECT e.last_name, e.department_id, d.department_nameFROM employees eFULL OUTER JOIN departments dON(e.department_id=d.department_id);

There is no direct comparable Oracle specific join

Marge Hohly 23

Example 4.4.5 Construct a join to display a list of Global

Fast Foods customers whether or not they have placed an order as yet and all the customers who have placed orders.

SELECT c.first_name, c.last_name, o.order_number,o.order_date, o.order_totalFROM   f_customers cLEFT OUTER JOIN f_orders oON   (c.id = o.cust_id);

Marge Hohly 24

Types of Joins Oracle Proprietary

Joins (8i and prior): Cartesian Product Equijoin Non-equijoin Outer join Self join

SQL: 1999 Compliant Joins: Cross joins Natural joins Using clause Full or two sided

outer joins Arbitrary join

conditions for outer joins