Discussion 03 (1)DBMS Accesss

7/29/2019 Discussion 03 (1)DBMS Accesss

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Discussion Session2013.02.08

by Keehyung KimUW-Madison Business School


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Main parts

Create four tables, set data type, and input data

Set Format correctly (percent, currency)

Set Input Mask for Phone field

Set validation rule for Email field

Extra credit

Add extra validation rules

Add extra fields and records


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Purpose

Prevent redundant data in database

Use data in more efficient way

Relational Database (a database using relationship)

RowID Student Program Course Credits Instructor1 Tom B.S. Buddhism 3 Buddha

2 Tom B.S. Database 3 Lazimy

3 Jenny PhD Database 3 Lazimy

4 Jenny PhD Buddhism 3 Buddha

5 Jenny PhD Chistians 3 Jesus

6 Jenny PhD Evolution 3 Darwin

SID Student Program1 Tom B.S

2 Jenny PhD

CID Course Credits Instructor1 Database 3 Lazimy

2 Buddhism 3 Buddha

3 Chistians 3 Jesus

4 Evolution 3 Darwin


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One-to-Many

Most frequently used relationship

The basic relationship in Access

One side should have a unique key

One-to-One

Both side should be linked by unique key fields

Many-to-Many

Access does not support direct Many-to-Many relationship

Need to make meta-table for this relationship

For example, tblOrderProductis meta-table for this relationship


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One-to-many

One-to-onemany-to-many


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Relationship between two fields within one table

Example: spouse relationship among customers

How-to

Add the same table one more time in Relationships window

Link two tables (the same table)

Go to Edit Relationship to see

correct relationship type


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In one-to-many relationship,

- Parent table: tblCustomer(one-side)- Child table: tblOrder(many-side)


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A Foreign Key is a field in a relational table that matches

a candidate key of another table.

The foreign key can be used to cross-reference tables.

Source: http://en.wikipedia.org/wiki/Foreign_key

Example

In previous slide, CID in tblOrder is Foreign Key.
http://en.wikipedia.org/wiki/Foreign_keyhttp://en.wikipedia.org/wiki/Foreign_key


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Give powerful limitation on editing

data to keep database consistent

Limitation given by Access

Cannot add a child record with a non-existing parent record

Cannot delete a parent record if it has child records

Cannot change a FK in child record if the FK does not have a

match in parent table

Cannot change a PK in parent record if linked with child records


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Cascade update

When you change a PK in parent record,

all linked FKs in child records will be changed, too

Cascade delete

When you delete a parent record,

all linked child records will be deleted, too

Results

Keep consistency of database But, be extremely careful! The data can be all gone by one click!

Do not use Cascade option on your project!


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Due date: before 9:55 am on Feb. 15 Main problems

Create relationships in Access

Understand the concept of PK and FK Create Self One-to-one relationship (Extra credit)

Submission

Your Access database file (.accdb)

Text file answering the five questions (.txt)

Electronically submit into Discussion Homework 2dropbox


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Related readings: Chapter 5

Documents

Discussion 03 (1)DBMS Accesss