One important activity when creating calculation views, is to express the relationships between the different data sources. Frequently, this is done by using joins.
A specific node type, the Join node, is used in modeling to define joins between one or more data sources.
In addition to the join node, the Star Join node, which is used to model a star schema, also defines one or several joins between a main data sources (fact "table") and the dimension calculation views.
For each Join node, you must define which columns of the two joined sources must participate in the join condition, as well as the join type. You can also specify the cardinality, with the help of the Propose Cardinality feature.
Sample Business Case and Data
To illustrate the behavior of the different types of joins in SAP HANA Cloud, consider the following tables:
The objective is to join these tables to retrieve the sales order amounts (facts) with the customer information, including the states in which the customers reside.
To begin with, you can make the following observations so that you will better understand the behavior of each join type that is illustrated in the next section:
Sales Order 8 does not have a customer master record.
Customer TOM does not have any orders.
State TX does not have a description.
No customer resides in Alabama.