Hi,
Stream Analytics does require to have at least one source coming from one of these 3 streaming sources: Event Hubs, IoT Hub, or Blob/ADLS. We don't support SQL as a streaming source at this time, that's why the query is not valid. For the query to be valid, you need to JOIN streams and reference data (e.g. to augment the stream), then you need to have data flowing in the streaming source to see output.
If you scenario is to get data from SQL to Power BI directly, you can actually directly connect Power BI to your SQL source.