One or more database tables may contain multiple copies of the same information (for example, a column that is repeated in several tables), and your table may need to be normalized.
Normalization reduces duplication in a relational database. For example, suppose the people in your company work at a number of offices. To normalize the database, consider placing information about the offices (such as its address and main telephone numbers) in a separate table, rather than duplicating all this information for every employee.
You can, however, take normalization too far. If the amount of duplicate information is small, you may find it better to duplicate the information and maintain its integrity using triggers or other constraints.
For more information about normalizing data, see Step 3: Normalize the data.