Database Programming

Section 15 – Oracle Proprietary Join Syntax and Review

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Join Commands Two sets of commands or syntax used to make

connections between tables in a database: Oracle proprietary joins ANSI/ISO SQL 99 compliant standard joins

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Oracle Proprietary Joins Cartesian Product Equijoin Non-equijoin Outer join Self join

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Oracle Proprietary Joins Oracle proprietary syntax uses a join condition

in the WHERE clause

SELECT table1.column, table2.column FROM table1, table2 WHERE table1.column1 = table2.column2;

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Joining multiple tables To join n tables together,

you need a minimum of n-1 join conditions.

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Oracle Proprietary joins Simple join or equijoin SELECT table1.column, table2.column

FROM table1, table2WHERE table1.column1=table2.column2;

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ANSI Standard Joins Cross joins Natural joins Using clause Join on Left and Right outer joins Full (two sided) outer joins Arbitrary join conditions for outer joins

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Equijoin “Simple” or “inner” join SELECT clause specifies columns names to

retrieve FROM clause specifies the tables to access WHERE clause specifies how tables are to be

joined An equijoin is a table join that combines rows

that have the same values for the specified columns

Example on next slide

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Equijoin

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Retrieving Records with Equijoins SELECT employees.employee_id,

employees.last_name, employees.department_id, departments.department_id, departments.location_id FROM employees, departments WHERE employees.department_id = departments.department_id;

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Equijoin SELECT d_play_list_items.song_id,

d_play_list_items.event_id, d_track_listings.cd_number FROM d_play_list_items, d_track_listings WHERE d_play_list_items.song_id = d_track_listings.song_id;

SONG_ID EVENT_ID CD_NUMBER

45 100 92

46 100 93

47 100 91

48 105 95

49 105 91

47 105 91

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Cartesian Product Join Joins 2 or more tables together without a join

conditions Joins every row in table 1 to every row in table

2 Number of resulting rows is M*N where M =

number of rows in table 1 and N = number of rows in table 2

You should avoid a Cartesian product by ALWAYS having a valid WHERE clause

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Cartesian Product Join Example EMPLOYEES (20 rows) SELECT employee_id,

last_name, depatment_idFROM employees;

DEPARTMENTS (8 rows) SELECT department_id,

department_name, location_idFROM departments;

Employee_id Last_name Department_id

100 King 90

101 Kochhar 90

201 Hartstein 20

202 Fay 20

Department_ID

Department_Name

Location_ID

10 Administration

1700

20 Marketing 1800

110 Accounting 1700

190 Contracting 1700

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Restricting rows in Join The Where clause can be used to restrict the

rows considered in one or more tables of the join. User AND operator to restrict the number of rows

returned in a join. Qualify the column in statement with the table

name or alias SELECT d_play_list_items.song_id,

d_play_list_items.event_id, d_track_listings.cd_number FROM d_play_list_items, d_track_listings WHERE d_play_list_items.song_id = d_track_listings.song_id AND d_play_list_items.event_id < 105;

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Using the AND operator SELECT last_name, employees.department_id,

department_name FROM employees, departments WHERE employees.department_id = departments.department_id AND last_name = 'Matos';

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Table Alias Simply typing lengthy statement using table

alias in place of table names. Define table alias in the FROM clause SELECT d_track_listings.song_id AS TRACK,

d_play_list_items.song_id AS " PLAY LIST" FROM d_play_list_items, d_track_listings WHERE d_play_list_items.song_id = d_track_listings.song_id;

Track Playlist

45 45

46 46

47 47

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Table Aliases Another way to make statements easier to

read is to use table aliases. A table alias is similar to a column alias; it renames an object within a statement. It is created by entering the new name for the table just after the table name in the from-clause. However, if a table alias is used in the FROM clause, then that table alias must be substituted for the table name throughout the SELECT statement.

SELECT p.song_id , t.song_id FROM d_play_list_items p, d_track_listings t WHERE p.song_id = t.song_id;

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Nonequijoin A non-equijoin than is a join between two tables

when column values in each table match a range of values but is not an exact match

Retrieve data from a table that has no corresponding column in another table.

= operator can not be used by itself Can use <=, >=, BETWEEN…AND BETWEEN…AND most effective SELECT p.code, e.cost

FROM d_packages p, d_events eWHERE e.cost BETWEEN p.low_range AND p.high_range;

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Outer Join Outer join is used to see rows that have a

corresponding value in another table plus those rows in one of the tables may have missing data

Use a plus (+) after the table’s column name in the WHERE clause of the query

Outer join cannot use the IN operator or be linked to another condition by the OR operator

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Example SELECT d.department_id, e.last_name

FROM employees e, departments d WHERE e.department_id = d.department_id (+);

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Join with a Plus sign (cont.) SELECT table1.column, table2.column

FROM table1, table2 WHERE table1.column(+) = table2.column;

SELECT table1.column, table2.column FROM table1, table2 WHERE table1.column = table2.column(+);

SELECT table1.column, table2.column FROM table1, table2 NEVER table1.column(+) = table2.column(+);

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Join with plus sign Use the plus sign to indicate the table whose

column is missing data SELECT a.column, b.column

FROM table1 a, table2 bwith on of the following WHERE clauses

WHERE a.column(+) = b.column WHERE a.column = b.column(+) NEVER WHERE a.column(+) = b.column(+) CAN’T use IN operator or OR operator in

WHERE clause

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