Databases

Databases

1. Tables

   • Information stored in tables, from a few to a million records
   • Row is a record, column is a field
   • Tables store records for a particular category
   • Flat-file database has just one table

2. Records + Fields

   • Record is all data about one person/thing
   • Field is one piece of data about person/thing
   • Field lengths are managed to save space
   • Each character takes up one byte, so keeping at default takes up too much space

3. Data Types

   • Alphanumerical or Text (text, numbers and symbols)
   • Number (whole number or decimal)
   • Currency (with symbol and 2 decimal places)
   • Date/Time (restricts input)
   • Autonumber (increases by 1 as record added)
   • Logical (true/false)
   • Boolean (one or the other)
   • Yes/No

4. Keys

   • Primary key is used to identify each record e.g. candidate number
   • Foreign key links tables together and creates a relationship.
     • Could be a field in one table, and a primary key in another
     • If you wanted to change teacher name, just change it in one table and the rest change automatically

5. Referential Integrity - ensures related records cannot be deleted