1. Agenda for 02/21/2006 Learn how to use more than one table in a query. Discuss how DBMS processes multiple tables. Explain the different types of joins. Describe join conditions. Do lab exercise

2. Sample Database ERD Assume referential integrity is NOT maintained in this database

3. Vocabulary Words Select List Result Table Join Cartesian Product/Cross Join Join Condition Multiple Table Access SELECT * FROMemp, time;

4. Combining Tables Based on a Shared Column (newer syntax – using join condition) SELECTname, contractid, datetime, amount/60 FROMtime INNER JOINemp ONtime.empid = emp.empid

5. Viewing all rows from one of the tables in a join (newer syntax using join condition) SELECTname, time.empid contractid, datetime, amount/60 FROMtime LEFT OUTER JOINemp ONemp.empid = time.empid Imagine that the time table is “left” (because it is declared first) and the emp table is “right” (because it is declared second)

6. Right outer join – Viewing all rows in other table (newer syntax using join condition) SELECT name, time.empid, contractid, datetime, amount/60 FROM time RIGHT OUTER JOINemp ON time.empid = emp.empid ; Remember that the time table is “left” (because it is declared first) and the emp table is “right” (because it is declared second)

7. Full outer join – Viewing all rows in both tables (newer syntax using join condition – option 1 is not available) SELECTname, time.empid, contractid, datetime, amount/60 FROM time FULL OUTER JOINemp ON time.empid = emp.empid;

8. SELECTemp.name, time.empid, time.worktypeid, work.description, datetime, amount/60 FROMtime INNER JOINemp ONtime.empid = emp.empid INNER JOINwork ONtime.worktypeid = work.worktypeid; Combining more than two tables into a single result table

9. Displaying all data in TIME table COLUMN emp_name heading “Employee Name” COLUMN descr heading “Type of Work” SELECT NVL(emp.name,'NOT IN EMPLOYEE TABLE') emp_name, time.empid, time.worktypeid, NVL(work.description,'NOT IN WORK TABLE’) descr, datetime, amount/60 FROMtime LEFT OUTER JOINemp ONtime.empid = emp.empid LEFT OUTER JOINwork ONtime.worktypeid = work.worktypeid ORDER BYemp.name;

10. Adding a standard condition SELECT NVL(emp.name,'NOT IN EMPLOYEE TABLE') emp_name, time.empid, time.worktypeid, NVL(work.description,'NOT IN WORK TABLE’) descr, datetime, amount/60 FROMtime LEFT OUTER JOINemp ONtime.empid = emp.empid LEFT OUTER JOINwork ONtime.worktypeid = work.worktypeid WHERE datetime BETWEEN ’01-jan-2006’ and ’15-jan-2006’ ORDER BY emp.name;

11. Summarizing Data COLUMN descr heading “Type of Work” SELECT NVL(work.description, ‘No Description’) descr, round(sum(amount/60),2) FROM time LEFT OUTER JOIN work ON work.worktypeid = time.worktypeid GROUP BY work.description ; The GROUP BY statement is frequently used with a result table created by multiple underlying tables

12. Recursive Relationship with Employee to Assign Manager

13. Self-join also called a recursive join (newer syntax using join condition) SELECTworker.empid "worker#", worker.name "worker name", manager.empid "manager#", manager.name "manager name" FROMemp worker INNER JOINemp manager ONworker.mgrid = manager.empid; What change is necessary to make all employees appear whether there is a manager?