In a relational Database, data is thought of in terms of logical sets of records.
- Each record is a mathematical tuple, but thought of as a row in a table.
- The parts of the record, the fields are the columns of the table.
- The logical sets (tables) are related to each other through key values stored as a column in each table that is related.
- Each data value is held only once. The name of a Customer John Smith should only be held once
- Data Independence
- It is efficient for disk space, processing, User friendliness, development.
- An Industry standard
When creating a table the data inputs need to be specified. This can be done using the following constraints
Null and Not Null;
Not Null forces a value to be inputted by the user or a unique number created. Null means that the record can be left empty with no data inserted. Null should only be used in extreme cases. A value should always be used so when sorting and exporting data Null can corrupt the results sometimes.