--zad. da ne se dopuska promqna na MovieExec(insert, update, delete),
 --ako srednata stoinost na Networht stawa pod 500 000
 create trigger tr
 on MovieExec
 alter insert,update,delete
 as
 if(select avg(networth) from MovieExec) < 500000
 begin 
 raiserror('...',16,1)
 rollback
 end