Read part 1 of this tip.
In the last tip we talked about what is a "fan trap" in a business intelligence application. Here we discuss the automated resolution for
Discoverer comes with fan trap detection capability in its client tool. Each user can choose to enable or disable this feature.
- If your query contains only aggregates on the tables you are joining, then Discoverer will handle the aggregate calculations by rewriting your query for you -- very nice!
- If, however, your query contains details from those tables you are joining, then Discoverer will prevent you from doing this.
Here are some guidelines if you are running Oracle Discoverer:
- When developing reports, leave fan trap detection enabled. This ensures that you do not create a fan trap. Of course this means that you may have to rewrite your query once you are warned by Discoverer that you have one. However, if the fan trap cannot be removed, then checking the "disable" box will permit you to continue working on the report.
- When testing check "disable fan-trap detection" and leave it checked; it does not interfere with reports that do not incorporate fan traps and permits you to run those that do.
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This was first published in September 2002