如何使用if语句MySQL生成delete和adding的触发器？

有两个表的队列（预约id、实际时间）队列摘要（日期、医生id、患者数量）

第一个是所有的队列，第二个是某个日期每个医生的队列数量。我需要构建一个触发器来更新患者的数量，每次在队列中添加队列时，我都需要在该日期将患者的数量添加到医生。拆卸时也是如此

我刚刚计算了给定医生id和日期的队列数量，将其分为两个触发器。 但我唯一的问题是，我应该将if语句放在何处，该语句检查此日期是否在Queue_Summary上，如果不在，则添加它

（另一方面，我不是100%支持thoes，因为我的数据库有点混乱，存在很多问题，如果thoes有任何问题，我会很高兴让他们知道）

---

您应该在触发器中执行生存测试。比如说

drop table if exists queue,queue_summary;
create table queue  (appointment_id int auto_increment primary key, doctor_id int,actual_time datetime);
create table Queue_Summary (date date, doctor_id int, num_of_patients int);

delimiter $$
create trigger ut after insert on queue
for each row 
begin
    if not exists (select 1 from queue_summary where date = date(new.actual_time) and doctor_id = new.doctor_id)  then
        insert into queue_summary values(date(new.actual_time),new.doctor_id,1);
    else
        update queue_summary
            set num_of_patients = num_of_patients + 1
            where date = date(new.actual_time) and doctor_id = new.doctor_id;
    end if;
end $$

delimiter ;

insert into queue (doctor_id,actual_time) values(1,'2020-05-03 09:00'),(1,'2020-05-03 09:30');

select * from queue;
select * from queue_summary;

MariaDB [sandbox]> select * from queue;
+----------------+-----------+---------------------+
| appointment_id | doctor_id | actual_time         |
+----------------+-----------+---------------------+
|              1 |         1 | 2020-05-03 09:00:00 |
|              2 |         1 | 2020-05-03 09:30:00 |
+----------------+-----------+---------------------+
2 rows in set (0.001 sec)

MariaDB [sandbox]> select * from queue_summary;
+------------+-----------+-----------------+
| date       | doctor_id | num_of_patients |
+------------+-----------+-----------------+
| 2020-05-03 |         1 |               2 |
+------------+-----------+-----------------+
1 row in set (0.001 sec)

删除触发器与此类似，但更简单

delimiter $$
create trigger dt after delete on queue
for each row 
begin
    if exists (select 1 from queue_summary where date = date(OLD.actual_time) and doctor_id = old.doctor_id)  then
        update queue_summary
            set num_of_patients = num_of_patients - 1
            where date = date(old.actual_time) and doctor_id = old.doctor_id;
    end if;

end $$

delimiter ;

---

存在性检查完全是装饰性的，因为如果没有什么可删除的，删除不会抱怨。

你没有接受@gordon linhoff昨天在回答中提供的任何内容-为什么？当我问他如何工作时，他没有重播，我只看到两个没有if的更新。。。无论需要做什么，这都是双重更新。我如何使用它？答案是否提供了令人满意的更新方式？你为什么不使用新的。而且很老。价值观请在问题中添加表定义和示例数据。不，因为这不是我的问题。我不明白你不能同时删除和插入。。。不管更新是否是我所需要的，它都是两个更新，一个是加1，另一个是减。意味着它什么也没做。如果我弄错了，请在我询问有关代码的更多信息时告诉我一些应该是新的。某些内容可能来自插入或更新行。假设select为您提供了所需的内容，那么应该更新哪一行？

drop table if exists queue,queue_summary;
create table queue  (appointment_id int auto_increment primary key, doctor_id int,actual_time datetime);
create table Queue_Summary (date date, doctor_id int, num_of_patients int);

delimiter $$
create trigger ut after insert on queue
for each row 
begin
    if not exists (select 1 from queue_summary where date = date(new.actual_time) and doctor_id = new.doctor_id)  then
        insert into queue_summary values(date(new.actual_time),new.doctor_id,1);
    else
        update queue_summary
            set num_of_patients = num_of_patients + 1
            where date = date(new.actual_time) and doctor_id = new.doctor_id;
    end if;
end $$

delimiter ;

insert into queue (doctor_id,actual_time) values(1,'2020-05-03 09:00'),(1,'2020-05-03 09:30');

select * from queue;
select * from queue_summary;

MariaDB [sandbox]> select * from queue;
+----------------+-----------+---------------------+
| appointment_id | doctor_id | actual_time         |
+----------------+-----------+---------------------+
|              1 |         1 | 2020-05-03 09:00:00 |
|              2 |         1 | 2020-05-03 09:30:00 |
+----------------+-----------+---------------------+
2 rows in set (0.001 sec)

MariaDB [sandbox]> select * from queue_summary;
+------------+-----------+-----------------+
| date       | doctor_id | num_of_patients |
+------------+-----------+-----------------+
| 2020-05-03 |         1 |               2 |
+------------+-----------+-----------------+
1 row in set (0.001 sec)

delimiter $$
create trigger dt after delete on queue
for each row 
begin
    if exists (select 1 from queue_summary where date = date(OLD.actual_time) and doctor_id = old.doctor_id)  then
        update queue_summary
            set num_of_patients = num_of_patients - 1
            where date = date(old.actual_time) and doctor_id = old.doctor_id;
    end if;

end $$

delimiter ;