ASA SQL User's Guide
Monitoring and Improving Performance
Top performance tips
In general, the information in each column of a table should depend solely on the value of the primary key. If this is not the case, then one table may contain multiple copies of the same information, 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 the generally good notion of 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.