on 02-23-2016 6:43 PM
Hello,
I have built a Star Join Model using a Customer Dimension Calc View in Star Join Node. In another Star Join Model, I am using the same Customer Dimension as a Normal Projection node and Joining it with Fact table using Left outer Join.
Ran a query to get just the Customer and all Key figures against both models. The explain plan for both queries was exactly same. The customer dimension view was not accessed unless additional attributes were requested from it.
Need some help in understanding Star Join Concept in above scenario. Why should I use Star Join in this case ?
Thanks,
MM
Hi Manav,
for the scenario you mentioned, your statement is correct.
//The explain plan for both queries was exactly same. The customer dimension view was not accessed unless additional attributes were requested from it.//
For the above case, Visualization plan exactly same for both left outer join case or star join case.
But Functionality wise different is there.
1. In Referential Join option is there in CV Star Join (Be Default it will be selected.)
If you select Columns from both Dimension CV and Fact Table
Star Join Case: Inner Join will be executed.
LO Join: Left outer join only will be executed.
2. In Star Join, we can able to join Multiple Dimension CV to the Fact Table in Single node.
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Hello,
Thanks for your input. Yes, joining multiple dimension CV in single node is one reason. However, there is an option to join the dimension using left outer join in star join. So if I select attribute from the dimension view which is joined in star join node using left outer, it will perform in same way.
One thing which I noticed when I requested additional attribute from the dimension CV.
For view created using join conditions, optimizer used OLAP engine along with calculation
For view created using STAR JOIN, all operations happened in calculation engine itself.
This could be a reason to use star join, so as to avoid transfer between different engines?
Thanks, MM
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