For further reference, WixData turns out to be actually a NoSql database (it is based on MongoDB). Hence joins operations are strongly discouraged by the API.
The task in the question may be resolved with two include s operations (one for Actors, one for Cinema), arranging then the elements with a single for-loop into a single array that can be given to the table. However include s only support up to 50 elements. The other alternative, i.e. using queryReferenced in the for-loop, also turns out to be infeasible: using it with a table containing 250 elements resulted in an error “Too many requests”.
Needless to say that it would be VERY appreciated if Wix said clearly that one cannot expect to use joins: this would actually save people’s worktime, contrary to the marketing junk.