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Message Posted: Tue, 24 Oct 2006 @ 20:20:31 GMT

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The most common mistake I see people make when first implementing join views is to include the same table in multiple views which are in turn expected to be joined together. Eg:

     View1: Table1, Table2, Table3
     View2: Table1, Table4, Table5

Each of these views by itself is fine but when the two views are joined together Table1 will be included and joined twice which is often not what the user intended and often causes significant performance issues (eg product join the two copies of Table1).

This happens frequently when people want to create views to show a star schema to users. Creating a view to join the snowflake dimensions together is great. Often though, people on their first cut will include the fact table in the view. Then when views for each dimension are joined together the fact table is included multiple times - causing great harm to performance and even wrong answers.

Pay close attention to how you expect the join views to be used, particularly if you expect them to be joined and avoid including tables which will end up with several copies from multiple views.

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