DAT602 – 07/03/2016

Relational Databases;

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

Why?

  • 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 constraintsData Types for DAT602.PNG

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.

 

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