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Databases
- A key feature of every table is that it has a
'primary key' for every record. A primary key
provides a way to uniquely identify every
record in a table.
- A foreign key is used to link tables
together and create a relationship.
It is a field in one table that is
linked to the primary key in
another table.
- Referential integrity forces the rule
that a primary key cannot be
duplicated in a table. It also ensures
that if the primary key one table is
changed, then the foreign keys in
the other tables are also updated.
- Rules can be put in place that forces field data to be in a
certain format. For example, a date field may have to use
dd/mmm/yyyy i.e. 02/Sep/2007 and not Sep 2nd 07 for
example. This is called data validation
- A relational database can avoid data duplication. It is
made up of two or more tables. Tables are related to one
another Each record in a table has a primary key. A foreign
key provides a link between records in different tables.
Data integrity ensures that data remains conistent across
tables.
- Check digit - the last one or two digits in a code
are used to check the other digits are correct.
Lookup table - looks up acceptable values in a
table
- Format check - checks the
data is in the right format.
Presence check - checks
that data has been entered
into a field
- Length check - checks the
data isn't too short or too long.
Range check - checks that a
value falls within the specified
range
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