I have a relational database:
Examination (ExaminationID, DetectedDisease, Name)
Uses (ReagentID, ExaminationID, ReagentQuantity)
Reagent (ReagentID, Name, Stock, MinimumPermissibleStock)
Examined (InsuranceNumber, ExaminationID, ExaminationDate, Results, TakenResults?)
I want to create a function that when a new record of "examined" is added the quantity of the reagent that examination uses to be substracted from "reagent.stock". Also when reagent.minimumPermissibleStock is lower than stock to return a warning message.
For the second part of the problem i tried this, but it does not work:

create function warning() returns trigger AS $warning$ begin if reagent.new.stock < reagent.minimumPermissibleStock then raise exception 'Probably mistake'; end if; return new; end;$warning$ LANGUAGE plpgsql;Thanks in advance


Check Solution