Could not determine output schema for query due to error

Hello community,
I get an error response when I just try to use the ksql example from the confluent page:

CREATE TABLE foo AS
SELECT * FROM bar
WINDOW TUMBLING (size 10 seconds)
EMIT CHANGES;

Response:
"Could not determine output schema for query due to error: Line: 3, Col: 8: WINDOW clause requires a GROUP BY clause. "

Why do I net a group by clause there?

Thank you in advance!