Returns True if this DataFrame contains one or more sources that
continuously return data as it arrives. A DataFrame that reads data from a
streaming source must be executed as a StreamingQuery using the start()
method in DataStreamWriter. Methods that return a single answer, (e.g.,
count() or collect()) will throw an AnalysisException when there
is a streaming source present.
New in version 2.0.0.
This API is evolving.