9.1 Databases
Data Types
There are a number of data types that are represented in a database:
Text (e.g. NG321AE)
Character (e.g. X)
Boolean (e.g. True)
Integer (e.g. 15)
Real (e.g. 19.33)
Date / Time (e.g. 180555)
Primary Keys
Each table has a primary key. It acts as a unique number. Duplicate data items would be deleted if entered into the primary key field. It identifies each individual record.
SQL
Command
Explanation
SELECT
Which fields you want to display
FROM
The table where the data is stored
WHERE
The search criteria
ORDER BY
The data is ordered with rules
SUM
To add numerical data
COUNT
To count the items of data
ASC
Order in ascending order
DESC
Order is descending order
*
Use all fields
<>
Equal to
Exam Questions
Last updated