PostgreSQL中的条件更新和选择语句

Question

我正在postgresql中创建一个计划表。我希望用户能够更新一行中的任何列。如果用户仅更改一个值，则希望更新该值，而所有其他值保持与数据库中相同。我尝试做一个直接的update语句，任何未定义的输入都会将列值更改为null。

这是我的解决方案

create table schedule (
    id serial primary key,
    instructor_id integer references users(id),
    holidays boolean, 
    sunday_morning text,
    sunday_afternoon text,
    monday_morning text,
    monday_afternoon text,
    tuesday_morning text,
    tuesday_afternoon text,
    wednesday_morning text,
    wednesday_afternoon text,
    thursday_morning text,
    thursday_afternoon text,
    friday_morning text,
    friday_afternoon text,
    saturday_morning text,
    saturday_afternoon text
);

插入声明

insert into schedule (
    instructor_id,
    holidays, 
    sunday_morning,
    sunday_afternoon,
    monday_morning,
    monday_afternoon,
    tuesday_morning,
    tuesday_afternoon,
    wednesday_morning,
    wednesday_afternoon,
    thursday_morning,
    thursday_afternoon,
    friday_morning,
    friday_afternoon,
    saturday_morning,
    saturday_afternoon
) values (2, false, null, '7 - 9', null, null, '4 - 7', null, null, null, '9 - 11', null, null, null, null, null )

更新声明

update schedule 
set 
    holidays = case when true <> NULL then true else holidays end ,
    sunday_morning = case when 'asd' <> NULL then 'asd' else sunday_morning end,
    sunday_afternoon = case when 'asd' <> NULL then 'asd' else sunday_afternoon end,
    monday_morning = case when 'asd' <> NULL then 'asd' else monday_morning end,
    monday_afternoon = case when 'asd' <> NULL then 'asd' else monday_afternoon end,
    tuesday_morning = case WHEN 'asd' <> NULL then 'asd' else tuesday_morning end,
    tuesday_afternoon = case when 'asd' <> NULL then 'asd' else tuesday_afternoon end,
    wednesday_morning = case WHEN 'asd' <> NULL then 'asd' else wednesday_morning end,
    wednesday_afternoon = case when 'asd' <> NULL then 'asd' else wednesday_afternoon end,
    thursday_morning = case when 'asd' <> NULL then  'asd' else thursday_morning end,
    thursday_afternoon = case when  'asd' <> NULL then 'asd' else thursday_afternoon end,
    friday_morning = case when  'asd' <> NULL then  'asd' else friday_morning end,
    friday_afternoon = case when  'asd' <> NULL then  'asd' else friday_afternoon end,
    saturday_morning = case when  'asd' <> NULL then  'asd' else saturday_morning end,
    saturday_afternoon = case when  'asd' <> NULL then  'asd' else saturday_afternoon end
where instructor_id = 1
select * from schedule

asd只是伪数据。我不知道为什么会破裂。 我尝试了较小的规模，并且效果很好，但是现在却抛出了错误。