double_book_keeping.sql

CREATE OR REPLACE FUNCTION fa.double_book_keeping_check() RETURNS trigger
AS $$
BEGIN
    IF TG_TABLE_NAME='reports' THEN 
        IF NEW.total_assets = (NEW.total_equity + NEW.total_liabilities) THEN
            RETURN NEW;
        ELSE
            RAISE EXCEPTION 'BOOK KEEPING ERROR: TOTAL ASSETS DOES NOT MATCH SUM(TOTAL LIABILITIES, TOTAL EQUITY)!';
        END IF;
    END IF;
END;
$$ LANGUAGE 'plpgsql';

CREATE TRIGGER book_keeping_check 
    BEFORE INSERT OR UPDATE ON fa.reports
    FOR EACH ROW
EXECUTE PROCEDURE fa.double_book_keeping_check();