更新 Postgresql 中的多个列

Question

我有一个名为 Availability(uname, date, start_time, end_time) 的表，用户可以在其中输入他们空闲的时间段。 现在我想在插入或更新可用性表之前创建一个触发器，以检查新输入是否与同一用户在同一日期的现有可用性重叠。 如果重叠，我想合并两个时隙。 到目前为止，这是我的代码：

create or replace function check_overlap()
returns trigger as $$
begin
    update availability a0
    set (a0.start_time, a0.end_time) =
        case (select a.start_time, a.end_time from availability a where a.uname = new.uname and a.start_date = new.start_date)
            when NEW.start_time < a0.start_time and NEW.end_time < a0.end_time then row(NEW.start_time, a0.end_time)
            when NEW.start_time > a0.start_time and NEW.end_time > a0.end_time then row(a0.start_time, NEW.end_time)
            when NEW.start_time < a0.start_time and NEW.end_time > a0.end_time then row(NEW.start_time, NEW.end_time)
            when NEW.start_time > a0.start_time and NEW.end_time < a0.end_time then row(a0.start_time, a0.end_time)
        end;
end;
$$ language plpgsql;

create trigger tg_INSERT_UPDATE_avail
before insert or update
on availability
for each row
execute function check_overlap();

现在，问题是我面临这个错误：

ERROR:  source for a multiple-column UPDATE item must be a sub-SELECT or ROW() expression
LINE 3:   case (select a.s_time, a.e_time from availability a where ...
          ^

任何见解表示赞赏！

Answer 1

您可以简单地将SELECT移到CASE语句之外：

update availability a0 set (a0.start_time, a0.end_time) = (
    select case when NEW.start_time < a0.start_time and NEW.end_time < a0.end_time then row(NEW.start_time, a0.end_time)
        when NEW.start_time > a0.start_time and NEW.end_time > a0.end_time then row(a0.start_time, NEW.end_time)
        when NEW.start_time < a0.start_time and NEW.end_time > a0.end_time then row(NEW.start_time, NEW.end_time)
        when NEW.start_time > a0.start_time and NEW.end_time < a0.end_time then row(a0.start_time, a0.end_time)
        else row(NEW.start_time, NEW.end_time)
    end
    from availability a where a.uname = new.uname and a.start_date = new.start_date
);

顺便说一句：我无法对此进行测试，但没有 where 子句的更新对我来说看起来很奇怪。