如何使用 if 語句 MySQL 觸發刪除和添加？

Question

有兩個表的 Queue (appointment_id, actual_time) Queue_Summary (date, doctor_id, num_of_patients)

第一個是所有隊列，第二個是每個醫生在某個日期的隊列數。 我需要構建一個更新 num_of_patients 的觸發器，每次在隊列中添加隊列時，我都需要在該日期添加到醫生 num_of_patients。 拆的時候也是。

我剛剛計算了給定醫生 ID 和日期的隊列數量，並將其分為兩個觸發器。 但我唯一的問題是我在哪里放置 if 語句來檢查這個日期是否在 Queue_Summary 上，如果沒有則添加它。

（PS - 我不是 100% 的，因為我的數據庫有點關閉並且有很多問題，如果在 thoes 聲明中有任何問題，我會更樂意知道）

delimiter //
 CREATE TRIGGER update_queue_summary 
    AFTER DELETE ON queue
    FOR EACH ROW
        BEGIN
            update queue_summary as qs set num_of_patient = ( 
                select count(appointment_id) 
                from queue as q join appointment as a on appointment_id
                where a.doctor_id=qs.doctor_id and date(qs.actual_time)=date(qs.date())
                group by appointment_id
                ) where doctor_id=qs.doctor_id and date(qs.actual_time)=date(qs.date());
       END;//
 delimiter ;

delimiter //
 CREATE TRIGGER update_queue_summary 
    AFTER insert ON queue
    FOR EACH ROW
        BEGIN
            update queue_summary as qs set num_of_patient = ( 
                select count(appointment_id) 
                from queue as q join appointment as a on appointment_id
                where a.doctor_id=qs.doctor_id and date(qs.actual_time)=date(qs.date())
                group by appointment_id
                ) where doctor_id=qs.doctor_id and date(qs.actual_time)=date(qs.date());
       END;//
 delimiter ;

Answer 1

您應該在觸發器中執行存在測試。 例如

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)

刪除觸發器類似但更簡單

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 ;

存在檢查完全是裝飾性的，因為如果沒有要刪除的內容，刪除不會抱怨。