1. Inner Join vs. Outer Join
Information Retrieval from Relational Databases

2. Query Languages Relational Algebra Structured Query Language (SQL)
Three main operators: Select, Project, Join
Provides the conceptual basis for SQL and QBE
Structured Query Language (SQL)
The user enters commands according to a pre-defined syntax to retrieve desired data.
Query By Example (QBE)
The user starts with a sample of the table(s) columns and marks the fields he or she wants to include in the answer.
Defaults are available for summarizing and manipulating the data.

3. SQL (Structured Query Language)
Each query statement follows the same structure: SELECT attribute name(s) FROM table name(s) WHERE criteria is met;

4. Relational Algebra Select Project Join
includes only certain rows from a database table in its “answer”.
Project
includes only certain columns from a database table in its “answer”
Join
combines two or more database tables on the basis of one or more common attributes

5. Join Types Inner join(default in access) Outer join
includes only the records from both tables that have the exact same values in the fields that are joined
I.e.,
Outer join
includes all records from one table, and matches those records from the other table for which values in the joined fields are equal
Left Outer Join
Right Outer Join

6. Example Tables

7. Relationship View

8. Query to List ALL Employees and Description of any Training Courses Taken ( Inner Join)

9. Note: We have 6 employees
Example Tables
Note: We have 6 employees

10. Does this This Give Us What we Need?
The above based upon the default join which is the inner join and will not give us employees that have not taken training classes
SQL code created by access for QBE on previous slide

11. Using Outer Joins
Note change

12. SQL code created by access for QBE on previous slide

13. The Revenue Cycle of M&M
M&M sells its agleclaps to customers through a network of company salespeople. Each type of agleclap is bought from a particular vendor and is given an initial list price. Each salesperson services a separate group of customers and is allowed to offer them various discounts from list to induce sales. Each sale can include one or more types of agleclaps and can be paid for in any one of three ways: (1) immediately in cash, (2) on the 15th of the following month, or (3) over the course of six months. When cash is received, a cashier deposits it into a company bank account. Sales are signaled by invoices; cash receipts by remittance advices

15. Relationship View

16. Example Tables (Incomplete Enterprise Database) from Dunn & McCarthy (2004) working paper

17. SQL and Relational Algebra Inner Join vs. Outer Join
Find all details of all sales and the cash receipt number and amount applied of any cash receipts related to those sales
Data we need for this example is in 2 tables
Summary sales totals have been stored in sales table
If summary figure not stored, you would need also need the sale-inventory relationship table to calculate sales totals
Note: there have been no cash receipts related to sales transaction 6 & 7.
We examine here the same example for which we previously needed a Left Outer Join of Sale and Sale-CashRecDuality. The equivalent SQL statement and query result are shown. Notice that the Left Outer Join is accomplished in the FROM and WHERE clauses of the SQL statement.

18. Relational Algebra Inner Join in QBE Details of all sales, related cash receipts

19. Relational Algebra Inner Join in QBE Details of all sales, related cash receipts

20. Default join is inner Join
If you double click on the join you will see the join properties box.
Item 1, the inner join is the default

21. Inner Join Results
Sales transactions 6 & 7 are not listed since there was no cash receipts associated with them.
Does this create a potential problem??
SELECT Sale.SaleNumber, Sale.Amount, Sale.Date, Sale.CustomerNumber, [Sale-CashRecDuality].RemittanceAdviceNumber, [Sale-CashRecDuality].Applied FROM Sale INNER JOIN [Sale-CashRecDuality] ON Sale.SaleNumber = [Sale-CashRecDuality].SaleNumber;

22. Relational Algebra Outer Join in QBE Details of all sales, related cash receipts
Double-click on the join line

23. Relational Algebra Outer Join in QBE Details of all sales, related cash receipts
Click on appropriate join type
Click OK

24. Relational Algebra Outer Join in QBE Details of all sales, related cash receipts
Note change in Join line

25. Relational Algebra Outer Join in QBE Details of all sales, related cash receipts
Result

26. Joins Compared
Outer Join
Inner Join