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Transcript of Data Types
Different Data Types
> Numeric Data
- Real Numbers
> Alphanumeric (Text) Data
> Date and Time Data
> Boolean (Logical) Data
Alphanumeric (Text) Data
> They are datas that are made up of :
Date and Time Data
- It is formatted in a specific way which depends upon the setup of the computer, the software in use and the user's preferences.
Boolean (Logical) Data
- Sometimes called the yes/no data in some computer software
- It only have 2 values:
> TRUE or FALSE
> YES or NO
> ON or OFF
- It's a whole number
- Doesn't have a decimal or fractional parts
- Can be positive or negative
- It's number that can be placed in the number line (Integers and numbers with decimal/fractional parts), can be negative or positive
- They are real numbers that are formatted in a specific way.
- Shown with a currency symbol & 2 decimal places
- They are fractional real numbers (formatted in a specific way --> out of 100 , & with a percent symbol)
> Text data are ften input to a computer with speech marks ("...") around it
Selecting Data Types
- Before inputting data into the computer, we must analyse it and select the appropriate data types for each values
> It's usually referred to as a database
. A database is a collection of records
. A record is the set of data associated with a single object or person
. A data in each record is different, but ech record has the same structure (fields)
. Each field has a field name, which would be the label
. It would contain different data in each of the records
Key Field / Primary Key
It's really important that every record in a database can be individually identified. The ID number or a code is the ideal field to use to uniquely identify each individual record and be used as a Key Field or a Primary Key.
Viewing A Database
It is quite common to view the contents of a database as a table instead of one record at a time. A tabular view is compact and allows you to see a lot of records at once. It is also exactly the view you see when working with database softwares such as Microsoft Access.
> Each row of the table corresponds to a database record
> The column headings correspond to the database field names
> Each cell of the table corresponds to a field, and contains an item of data
A 'flat-file' database only contains a single table of data which is stored in one place
A 'relational' database contains two or more tables of data, connected by links called relationships.
Repeated data in a database is generally considered a bad thing:
- It wastes space in the database
- It takes time to input, typing the same data over and over (and mistakes may be made)
- It is a pain to update
HOW TO AVOID THIS?
read next page...
The solution is to split the data: The repeating data is removed from the main table, and placed in a table of its own. Now both tables are independent, and each one has its own key field / primary key.
Linking Tables (Relationships)
The common field in both tables is the Class field.
We use this field to create a relationship (link) between the two tables.
To create the relationship, we are using the key field (primary key) from one table to link it to another.
When a key field from one table appears in a different table, we call this a foreign key.
by: Andrea H