1. Unit 16 – Database Systems
Creating Tables
Unit 16 – Database Systems

2. Planning Your Table Before you create the table you must plan:
What fields you will include
What the data-types of those fields will be
What names to give them
Which field to use as the primary key
The range of acceptable values for each field
This is important as changes may be difficult later
You can plan a table design using a data dictionary
Creating Tables Presentation Unit 16

3. Data-type Each field must have a data-type
Choosing the correct data-type is important
Helps ensure only valid data is entered
Allows you to use features related to the data-type
Commonly used data-types are:
Text
Number
Date
Yes/No
Creating Tables Presentation Unit 16

4. Other Field Settings
As well as setting the name and data-type of a field there are other settings you can make.
Most of the settings are dependant on the data-type
Typical settings you might change include:
Field length
Format (e.g. date format, 20/7/05 or 20th July 2005)
Default value
Validation rule
Creating Tables Presentation Unit 16

5. Text Data-type
Use where text or text combined with numbers will be stored in the field
Also used to store numbers that don’t require calculations to be done (e.g. phone numbers)
Default length is 50 characters, maximum length is 255 characters.
For longer text use the Memo data-type
No preset formats
Creating Tables Presentation Unit 16

6. Numeric Data-type Field size
Not set as a value (e.g. 10 digits) but as a method of storage
This sets the range of values that can be stored
Integer – range of minus 32,768 to plus 32,768
Long Integer - range of minus/plus 2 million
Double stores very large real numbers.
Format
Allows formats such as
Fixed number of decimals
Scientific
Percent
Currency
Creating Tables Presentation Unit 16

7. Auto-number Special numeric data-type
Automatically set to long integer – don’t change it.
Automatically incremented by 1 when a new record is created
Ensures every record in a table has a unique value for this field
Ideal for primary key fields
BUT you cannot modify values in this field
Creating Tables Presentation Unit 16

8. Date/time data-type Used to store dates and or times
Will not allow input of invalid values (e.g. 32/7/05)
Various preset formats
Order of the day, month and year is set by Regional Settings in Control Panel.
Default value can be a fixed date or the =Now() function will insert the current date when inserting new records.
Creating Tables Presentation Unit 16

9. Example
You are creating a database of secondary school student details and you want a field to hold the student’s age on the 1st September in the current year
What data-type should you choose?
What field length?
Would a default value be a good idea?
Are there any validation rules you could add?
Creating Tables Presentation Unit 16

10. Example The data-type should be Numeric Field length should be Integer
Default value is probably not a good idea here
Validation rule could be added to restrict values to greater than 12 and less than 21
Creating Tables Presentation Unit 16

11. Data Dictionary Field name Data-type Field length Key? Format Default
Validation rule
Student number
Auto-number
Long integer
Yes -
Surname
Text 50 No
First Name
Date of Birth
Date
Short date
Gender 1
M or F
Creating Tables Presentation Unit 16