lesson 4:Database Tables

The core component of a database is a table. Data is defined and stored in a table. Multiple tables -- each consisting of different types of data -- can be created in a database.

Each row in the database is called a record. The entry for John Smith is called a record. The entry for Martha Tompkins is also a record. Each row or record is made up of columns or fields -- L.Name, F.Name, Phone, Address, City, State, Zip -- which contain a particular piece of information. 

L.Name F.Name Phone Address City State Zip 

Smith John 919.555.6320 100 Paramount Parkway Morrisville NC 27560 

Tompkins Martha 919.555.6427 97 Hummingbird Court Cary NC 27513 

Field Properties

Every table contains a number of columns called fields or datatypes. Fields are unique pieces of information that make up the information in a table. Tables usually contain multiple fields.
In a previous example we mentioned that a table might consist of the fields: Last Name, First Name, Phone, Address, City, State, and Zip. Each field has unique properties. Some contain characters. Others contain numbers. These Field Properties are defined when the table is created.

In a Contact Management database, a list of names -- those contacts to whom you have sent resumes or have met through your personal network -- might be maintained in a table, along with address, phone number, and other personal information.

Understanding Table Relationships

Databases can be simple -- consisting of a single table -- or made up of many different tables. If you were to convert your resume into a database, for example, you might have a table that contains your name and personal mailing address. We might call this the Contact_Information table.

Your work experience is a different kind of information. Instead of identifying who you are or where you live, it identifies the companies you worked for, their addresses, your job title, and responsibilities. Because this set of information is independent from the contact information, we might instead create a second table called the Work_Experience table.
The same is true of your educational background. It has no direct bearing on your contact information or the companies where you worked. A third table might be created called the Education table to save this kind of data.
The database contains three tables, each independent of the other, and all containing different types of information. The database needs a way to connect these three tables.

Primary Keys

Every table in Microsoft Access must have at least one field that uniquely identifies each record in the table. This field is known as a primary key. This primary key essentially opens the door to the table and allows you to retrieve information from the table.
The primary key is the mechanism by which you relate different tables and combine information for viewing (query) or printing (report).

Challenge!

Let us pretend that you are going to start your own home business. You are going to need to prepare a database for your business and the first step is to design a table that will contain a list of all your contacts that may one day be your clients or suppliers.
Let us assume that a database table called Business Contacts contains all the fields listed in the first column of the following chart. The chart also contains four other columns:

• Text, Numbers or Both -- should the field accept data entry input in the form of text, numbers, or both?
• Field Size -- the number of spaces you think the field should have.
• Required Entry -- should the field be required entry (the record cannot be added to the database without the information) or optional entry (a record can be added without entry in the field)
• Allow Duplicates -- should the database allow duplicate entries for the field (e.g., can several people in the database share the same zip code)?

Practice designing fields by filling out the following table.

	Text, Numbers, or Both?	Field Size	Required Entry?	Allow Duplicates?
First Name
Last Name
Company
Company Type
Address
City
State
Zip Code
Contact Id
Title
Work phone
Fax Number

Posted in: Access 2003