Database Programming

Sections 3 – Joins & Hierarchical Queries

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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

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Natural Join

ANSI/ISO SQL: 1999 Join equivalent of an equijoin

Join on all common columnsie. columns with same name and data type

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

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Example Natural Join

SELECT event_id, song_id, cd_numberFROM d_play_list_items NATURAL JOIN d_track_listingsWHERE event_id = 105;

Example Natural Join

SELECT first_name, last_name, event_date, descriptionFROM d_clients NATURAL JOIN d_events;

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FIRST_NAME LAST_NAME EVENT_DATE DESCRIPTION

Hiram Peters 14-May-04 Party for 200, red, white, blue motif

Lauren Vigil 28-Apr-04 Black tie at Four Season hotel

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Example

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.

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Cross Join

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

Syntax: SELECT *

FROM employeesCROSS JOIN departments;

Last section Cartesian Product:SELECT *FROM employees, departments;

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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 USING statement

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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);

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Example SELECT e.employee_id,

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

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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.

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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);

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Summary/Comparison

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Examples2. 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.

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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);

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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);

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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;

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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);

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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

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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

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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

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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

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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_totalFROM   f_customers cLEFT OUTER JOIN f_orders oON   (c.id = o.cust_id);

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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

On clause

Self-Join

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Self-JoinEmployee_id last_name manager_id employee_id last_name

100 King 100 King

101 Kochar 100 101 Kochar

102 De Haan 100 102 De Haan

103 Hunold 102 103 Hunold

104 Ernst 103 104 Ernst

107 Lorentz 103 107 Lorentz

124 Mourgos 100 124 Mourgos

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Manager_id in worker table = employee_id in Manager table

EMPLOYEES (worker) table EMPLOYEES (manager) table

Example SELECT chair.last_name || ‘ is the section chair of ‘ ||

player.last_nameFROM band_members chair, band_members playerWHERE player.chair_id = chair.member_id;

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Hierarchical Queries

Similar to the self-join Similar to an Organization Chart Shows company, department , family

structure etc.

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Using Hierarchical Queries

Retrieve data based on natural hierarchical relationships between rows

If data within a single table called tree walking

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Hierarchical queries

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EMPLOYEES as an organization chart

Kochar De Haan Mourgos

Hunold Rajs

Ernst

King

Hierarchical queries keywords

START WITH CONNECT BY PRIOR LEVEL

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Hierarchical queries keyword example

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Another example

SELECT last_name || ' reports to ' ||PRIOR last_name "Walk Top Down“FROM employeesSTART WITH last_name = 'King‘CONNECT BY PRIOR employee_id = manager_id;

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Results of query

Walk Top Down

King reports to

Kochhar reports to King

Whalen reports to Kochhar

Higgins reports to Kochhar

Gietz reports to Higgins

De Haan reports to King

Hunold reports to De Haan

Ernst reports to Hunold

Lorentz reports to Hunold

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Hierarchical query report

SELECT LPAD(last_name, LENGTH(last_name)+(LEVEL*2)-2,'_') AS ORG_CHARTFROM employeesSTART WITH last_name = 'King‘CONNECT BY PRIOR employee_id = manager_id;

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Hierarchical queries pruning

Delete branches of tree with WHERE clause or CONNECT BY PRIOR clause

WHERE - only row named is excluded CONNECT BY PRIOR – entire branch is

excluded View example on next slide

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Pruning Example

SELECT last_nameFROM employeesWHERE last_name <> 'Higgins‘START WITH last_name = 'Kochhar‘CONNECT BY PRIOR employee_id = manager_id;

Only the branch under King is returned

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Pruning Example

SELECT last_nameFROM employeesSTART WITH last_name = 'Kochhar‘CONNECT BY PRIOR employee_id = manager_idAND last_name <> 'Higgins';

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