Database Programming Sections 4 – Joins

Marge Hohly2 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 Hohly3 Cross Join  ANSI/ISO SQL: 1999 syntax for achieving of a Cartesian product  Syntax: SELECT * FROM employees CROSS JOIN departments; Last week: SELECT * FROM employees, departments;

Marge Hohly4 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, field2 FROM table1 NATURAL JOIN table2 WHERE fieldn = value;

Marge Hohly5 Example  SELECT event_id, song_id, cd_number FROM d_play_list_items NATURAL JOIN d_track_listings WHERE event_id = 105;

Marge Hohly6 Example Natural Join  SELECT employee_id, last_name, department_id, location_id FROM employees NATURAL JOIN departments;

Marge Hohly 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 Hohly8 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 Hohly9 Join Using  SYNTAX: SELECT field1, field2, field3 FROM table1 JOIN table2 USING(column name);  Example: SELECT e.employee_id, e.last_name, d.location_id FROM employees e JOIN departments d USING(department_id);

Marge Hohly10 Example  SELECT e.employee_id, e.last_name, d.location_id FROM employees e JOIN departments d USING(department_id);

Marge Hohly11 JOIN ON  ANSI/ISO: 1999 join clause that may be used to specify the condition or columns used:  Syntax: SELECT field1, field2, field3 FROM table1 JOIN table2 ON(table1.fieldx=table2.fieldy); SELECT e.last_name emp, m.last_name mgr FROM employees e JOIN employees m ON(e.manager_id = m.employee_id);  SELECT e.last_name as "EMP", w.last_name as "MGR“ FROM employees e JOIN employees w ON (e.manager_id = w.employee_id) WHERE e.last_name like 'H%'; Where clause can limit results.

Marge Hohly12 Example of JOIN ON  SELECT e.last_name, e.department_id, d.department_name FROM employees e JOIN departments d ON (e.department_id = d.department_id);

Marge Hohly13 Summary/Comparison

Marge Hohly14 Examples 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 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 Hohly15 Three-way Joins with the ON clause  A three-way join is the join of three tables  Syntax: SELECT employee_id, city, department_name FROM employees e JOIN departments d ON (d.department_id = e.department_id) JOIN locations l ON (d.location_id=l.location_id);

Marge Hohly16 Example  SELECT employee_id, city, department_name FROM employees e JOIN departments d ON (d.department_id = e.department_id) JOIN locations l ON (d.location_id=l.location_id);

Marge Hohly17 Revised example  SELECT e.employee_id, l.city, d.department_name FROM employees e, departments d, locations l WHERE e.department_id = d.department_id AND d.location_id = l.location_id

Marge Hohly18 INNER JOINS  An inner join returns only those rows that match the join condition SELECT e.last_name, e.department_id, d.department_name FROM employees e JOIN departments d ON (e.department_id = d.department_id);

Marge Hohly19 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 Hohly20 LEFT OUTER JOIN  SELECT e.last_name, e.department_id, d.department_name FROM employees e LEFT OUTER JOIN departments d ON(e.department_id=d.department_id);  SQL 99 equivalent: SELECT e.last_name, e.department_id, d.department_name FROM employees e, departments d WHERE e.department_id=d.department_id(+);  This statement will return those employees who do not have a department_id

Marge Hohly21 RIGHT OUTER JOIN  SELECT field1, field2.... FROM table1 a RIGHT OUTER JOIN table2 b ON (a.field=b.field); or USING(field name);  SELECT e.last_name, e.department_id, d.department_name FROM employees e RIGHT OUTER JOIN departments d ON(e.department_id=d.department_id);  This statement will return those departments who do not have any employees in them

Marge Hohly22 FULL OUTER JOIN  The FULL OUTER JOIN returns both matched and all unmatched rows  Syntax: SELECT field1, field2, field3 FROM table1 a FULL OUTER JOIN table2 b ON a.field=b.field; SELECT e.last_name, e.department_id, d.department_name FROM employees e FULL OUTER JOIN departments d ON(e.department_id=d.department_id);  There is no direct comparable Oracle specific join

Marge Hohly23 Example  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_total FROM f_customers c LEFT OUTER JOIN f_orders o ON (c.id = o.cust_id);

Marge Hohly24 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