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2mis6010-L Databases and Spreadsheets

2mis6010-L Databases and Spreadsheets. Lecturer Nishant Pithia. Week 5. Problem-solving and Revision for Database u sing Access Catch-up p ractical session for Week 1 – 4. Workshop 5 for MS Access - Report. Key Highlights from Previous Lectures. Stepwise database design Approach

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2mis6010-L Databases and Spreadsheets

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  1. 2mis6010-L Databases and Spreadsheets Lecturer Nishant Pithia

  2. Week 5 • Problem-solving and Revision forDatabase using Access • Catch-up practical session for Week 1 – 4. • Workshop 5 for MS Access - Report

  3. Key Highlights from Previous Lectures • Stepwise database design Approach • Simple Entity Relationship Diagram for database design • Entity; Its Attributes with data types • Making Assumption for relationship types • Constrains for Database Design • Entity Integrity (unique and non-null) • Referential Integrity (RI) and FK • Realise relationship in table view under the Constraints. ????? ?????

  4. Problems from Last Week • Queries last week: • Run query to Join tables for the order information of a particular customer (e.g. Anderson) • Run query to join multiple tables. • Problem: Retrieve no data

  5. Causes of the Problem • Causes: • Referential integrity is not enforced • Unmatched data types and properties between Primary Key (PK) and its corresponding Foreign Key (FK) • No value for FK Attributes/Fields, i.e. no matching values between tables • Use inappropriate matching fields between tables, i.e. even set non FK attribute as a matching field • Reasons: • Lack of full understanding of RI and FK

  6. Cause 1: Set Relationship without Enforcing Referential Integrity

  7. Run Query to Display Anderson’s Order

  8. Cause 1: Referential integrity is not enforced Where is Anderson???

  9. Benefit of Enforcing RI • Realize the relationship • Set Clear Matching Fields between tables • Automatically Check Matching Records for given relationship

  10. Cause: Unmatched data types between matching fields

  11. Cause 2: Unmatched data types between matching fields

  12. Enforced Referential integrity

  13. Run Query again ….Still No record!!!!!!!!?????

  14. Cause 3: Use inappropriate matching fields

  15. ONLY

  16. Now Query is working!!

  17. Implications and Reminders • Join Query joins tables by: • Finding the matching fields between tables based on FK and PK • Searching the matching values between the matching fields End of Problem-solving

  18. Recommended Approach for Assignment 1– Stage 1 Planning Stage 1: Planning on paper before entering data (i.e. Step 1 and 2 in Lecture 2) • Entity and Relationship mapping with clear assumptions and understanding of business cases. • Check some rules (fan shape connection?)

  19. Stage 1: Planning (cont’d) • Step 3 in the Lecture 2: • Plan for your tables view with PK and FK • Make sure: the table with PK in one end and the table with FK in many end Table with PK Table with FK

  20. Stage 2: From Paper to Access • Define each table (entity) with primary key, also foreign Key, other fields with their data types. • Make sure PK and FK have the same data types and properties

  21. Stage 2: From Paper to Access (Cont’d) • Create Relationship between the defined tables • Enforce the referential integrity

  22. Step 3 • Enter data to the table with PKin one end first, then to the table with FK in many end. • Avoid missing values • The values under the FK in a table must match those for PK in another table.

  23. Additional Notes for Assignment 1 • Tables with clear relationships • Interrelated tables with FK as the link • FK and corresponding PK have the same data types • Referential integrity is enforced • Query: make sure joining tables is working fine • Keep Form and Report simple and clear • Broad Reading for Relational Database

  24. Essential Reading • Colin Ritchie (2002), Relational Database Principle, 2nd Edition, Thomas Learning. • More books in Library

  25. Week 6 – 10 • Practical sessions on Ms Excel • Lectures by Request Reminders: • 7th December 2005 (Week 9) Deadline for DB Assignment!!! • Catch UP!! • Problems??? Drop in and see me!

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