Any query performs faster using a join index. The issue that must be examined is whether the benefit of the decreased response times provided by a join index offset the costs of its creation, maintenance, and storage.
The relative costs and benefits of defining a join index are described in Cost/Benefit Analysis for Join Indexes.
Computations that support cost/benefit analysis for join indexes include the following:
- Cost
- Benefit
- Benefit percentage
- Payback
- Query ratio