1. Database Programming Section 15 – Oracle Proprietary Join Syntax and Review 1

2. 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 2

3. Oracle Proprietary Joins  Cartesian Product  Equijoin  Non-equijoin  Outer join  Self join 3

4. 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; 4

5. Joining multiple tables  To join n tables together,  you need a minimum of n-1 join conditions. 5

6. Oracle Proprietary joins  Simple join or equijoin  SELECT table1.column, table2.column FROM table1, table2 WHERE table1.column1=table2.column2; 6

7. 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 7

8. 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 8

9. Equijoin 9

10. 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; 10

11. 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_IDEVENT_IDCD_NUMBER 4510092 4610093 4710091 4810595 4910591 4710591 11

12. 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 12

13. Cartesian Product Join Example  EMPLOYEES (20 rows)  SELECT employee_id, last_name, depatment_id FROM employees;  DEPARTMENTS (8 rows)  SELECT department_id, department_name, location_id FROM departments; Employee_idLast_nameDepartment_id 100King90 101Kochhar90 201Hartstein20 202Fay20 Department_IDDepartment_NameLocation_ID 10Administration1700 20Marketing1800 110Accounting1700 190Contracting1700 13

14. 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; 14

15. 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'; 15

16. 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; TrackPlaylist 45 46 47 16

17. 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; 17

18. 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 e WHERE e.cost BETWEEN p.low_range AND p.high_range; 18

19. 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 19

20. Example  SELECT d.department_id, e.last_name FROM employees e, departments d WHERE e.department_id = d.department_id (+); 20

21. 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(+); 21

22. 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 b with 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 22