Explanation/Reference:
Priority group
You can set priority group numbers to determine which logical table source should be used for queries for which there is more than one logical table source that can satisfy the requested set of columns.
For example, you might have user queries that can be fulfilled by both a data warehouse and an OLTP source. Often, access to an operational system is "expensive," while access to a data warehouse is
"cheap." In this situation, you can assign a higher priority to the data warehouse to ensure that all queries are fulfilled by the data warehouse if possible.
Note that the priority group of a given logical table source does not always ensure that a particular query will be fulfilled by that source.
Priority Group Designation
0 the highest-priority source (the default)
1 a lowest-priority source