Databases Letts Chapter 11

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

Ready-made database files are available on:  floppy disc,  CD-ROM’s  on-line using public networks

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.

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

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

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.

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) < (less than) > (greater than) <>, >=, <=  the logical operators AND, OR and NOT;  comparisons with sub-strings.

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.