May 27 2010

Everything About Shortcut Joins

Categories: Join Techniques, Universe Design Dave Rathbun @ 6:30 am

There have been a number of posts recently in the Semantic Layer forum on BOB about shortcut joins. When will they be used? How many can be used? Why won’t this particular shortcut get used? Do I have to add shortcuts to contexts? Lots of questions.

I am going to try to clear up a couple of those questions now. First here is a summary of everything I need to know about shortcuts:

  • Shortcut joins do not provide an alternate path.
  • Shortcut joins do provide a shorter path.

By the end of this post I hope that the reader will understand the difference between those two statements. There are two rules for how and when a shortcut will be applied:

  • A shortcut join will only be used if it eliminates tables from the query.
  • A shortcut join is applied after the SQL has been generated (meaning after a context selection has been made, if required).

I will talk about these two items as well. But first, how do I create a shortcut join in my universe? Continue reading “Everything About Shortcut Joins”