SQL-forespørgsler 00904. 00000 - %s:ugyldig identifikator

Du bør prøve små bogstaver for tabel-/kolonne-id'erne (som i from /inner join klausuler):

SELECT  entertainer_id,
        entertainer_groupname
FROM    casestudy_entertainer
INNER JOIN casestudy_availability ON casestudy_entertainer.entertainer_id = casestudy_availability.availability_entertainerid
INNER JOIN casestudy_calendardates ON casestudy_availability.availibility_calendardateid = casestudy_calendardates.calendar_id
WHERE entertainer_type = '&Entertainer_TYPE'
  AND casestudy_calendardates.calendar_date = '&Event_date'