trigger子查询必须只返回postgresql中的一列

Question

我已经设置了一个触发器，如下所示，但似乎发生了一些错误：

create or replace function insert_ft()
returns trigger as
$$
begin
    if ((select "WeekDay", "Time", sec."Quarter", sec."Year" 
        from "WeeklyMeeting" wm, "Section" sec
        where wm."SectionID" = new."SectionID"
        and wm."SectionID" = sec."SectionID")
        intersect
    (select "WeekDay", "Time", ft."Quarter", ft."Year"
     from "WeeklyMeeting" wm, "FacultyTeaching" ft, "Section" sec
     where sec."SectionID" = ft."SectionID"
     and ft."Quarter" = new."Quarter"
     and ft."Year" = new."Year"
     and ft."SectionID" = wm."SectionID"
     and "Name" = new."Name")) is not null
    then raise exception 'The Professor % has already taught a section %
    at % on %',
    new."Name", new."SectionID", (select "WeekDay" from "WeeklyMeeting"
        where "SectionID" = new."SectionID"), (select "Time" from "WeeklyMeeting"
        where "SectionID" = new."SectionID");
    else
    raise notice 'Adding Success';
    return new;
    end if;
end;
$$
language plpgsql;

create trigger "insert_constraint_ft"
before insert on "FacultyTeaching"
for each row execute procedure insert_ft();

错误显示为

ERROR:  subquery must return only one column
LINE 1: SELECT ((select "WeekDay", "Time", sec."Quarter", sec."Year"...

有人可以帮我查看错误发生的地方吗？谢谢！