2.3.1 Data Types

Numeric Data Types

Stored as Binary after converting from number

– For storing whole numbers – Can be either Positive or Negative (+ or -)

– For storing numbers when decimals are needed

– Usually 2 or 4 bytes

•Date / Time;
- For storing calender dates and times
  - Needed as time and date are not denary numbers
  - Units go up in different # days per month, 60 seconds to an hour, 24 hours to a day
- Used for either one or both together
- (Actualy converted to a number and then a binary value of data + time for storage)
•Currency:
- Used to store a specific 2 decimal number and display currency symbol
  - Includes 2 decimal places + a symbol
- (Used for all monetary values)

Question 1:

List all the date formats you know and calculate the max bytes each needs

Question 2:

What are the biggest & smallest values using 2 bytes in:

1.a) Pure Binary

2.b) Sign & Mag

3.c) Two’s Compliment

Alphanumeric Data Types

Character

String

Question 3: What is the longest name you know?

•Hint: Sri Lanken Cricketer

•

Boolean

–Used to store 'Either / Or' information; with only 2 possible values.

Many characters grouped together under a single identifier (e.g Name)
- Maximum number of charaacters defined by user
- The question is always;
  - What length / how many characters to store?
- Consider the longest possible value
  - •e.g. Mr Writhlington-Williamson

• Calculated Fields

–Not strictly a data type as they are not stored data

–just formula stored and calculated when needed

–e.g. to store Age as NOW() - DATE

• Question 4:

Why are telephone numbers are always stored as a string?

Further Reading