Databases

1
Databases

• Letts Chapter 11

2

• A database program can
• be used to
• sort a file into a different order
• search through the records for a matching string.
• select records which fit certain conditions

3

• Ready-made database files are available on
• floppy disc,
• CD-ROMs
• on-line using public networks

4

• Before you can create your own database file you
  have to
• decide what data is required for the problem you
  are solving
• think of a name for your data file
• plan what fields you are going to have
• decide on a key field or sort field
• plan how to collect and record the data before it
  is typed in.

5

• Common data types used in databases are
• alphanumeric
• number
• date
• integer
• label
• logical

6

• Data can be collected by recording it on a data
  capture form.
• This can be one of the following
• questionnaire (form format)
• table format.

7

• To create a database you would normally have to
• produce a data capture form
• collect and record the data to be keyed it
• run the database program
• name the database file
• key in for each field its name, type and
  possibly its length
• choose a sort field
• enter the data into the database - one
  record at a time
• close or save the database.

8

• To retrieve information from a file you can set
  up a query condition. The program then selects
  all records which match the condition.
• Query conditions can include
• comparisons based on
• (equal to)
• lt (less than)
• gt (greater than)
• ltgt, gt, lt
• the logical operators AND, OR and NOT
• comparisons with sub-strings.

9

• A sort rearranges a file into a given order.
• A file can be sorted into ascending or descending
  order.
• A database report is a set of results from work
  on a database put together as a document for
  printing.
• A query language is the set of words and symbols
  which are used to retrieve information from a
  database.