Keys
Table keys are used to identify records, and to speed up filtering and sorting. Having too few keys may result in painfully slow inquiries and reports. However, each key incurs a processing cost because the index containing the key must be updated every time information in a key field changes. Key cost is measured primarily in terms of increased index maintenance processing. There is also additional cost in terms of disk storage space (usually not significant) and additional backup/recovery time (sometimes very important).
When a system is optimized for processing speed, it is critical to analyze the SQL Server indexes that are active because that is where the updating and retrieval time are determined. The determination of the proper number and design of keys and indexes for a table requires a thorough understanding of the types and frequencies of inquiries, reports, and other processing for that table.
Every NAV table must have at least one key—the primary key. The primary...
