Use a GROUP BY clause or the nextval() function to connect a stream to a derived window as part of a complex query.
A derived window is a stateful element that requires a primary key, either explicit or deduced. When connecting a stream to a derived window, you assign a primary key one of two ways: using a GROUP BY clause or the nextval() function. Use the GROUP BY clause to aggregate column expressions from the stream to deduce a primary key when you compile the project in Studio. You cannot explicitly specify a primary key using the GROUP BY clause. Use the nextval() function to assign an explicit primary key in the absence of a GROUP BY clause.