Hi,
can anyone tell me what's wrong with this update query?

procedure P_MinutesOnMedium
lparameters tnMediumid

update medium ;
set total = select sum(length);
from film join recording on film.filmid = recording.filmid;
where recording.mediumid = tnMediumid;
where recording.mediumid = tnMediumid
endproc

thanks