如何使用 if 语句 MySQL 触发删除和添加？

Question

have two table's Queue (appointment_id, actual_time) Queue_Summary (date, doctor_id, num_of_patients)

The first is all the queues there are and the second is how many queues for each doctor on a certain date. I need to build a trigger that updates the num_of_patients, every time in Queue that a queue is added I need to add to a doctor num_of_patients on that date. Also when removing.

I have just counted the number of queues given a doctor_id and date, made it into two triggers. But the only problem I have is where do I place the if statement that checks if this date is on Queue_Summary and if not adds it.

(PS - Im not 100% on thoes also as my database is a bit off and does tons of problems, if there are any problem in thoes statments I'll be more them happy to know)

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

You should carry out an existence test in your trigger. For example

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)

And a delete trigger is similar but simpler

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 ;

The existence check is entirely cosmetic since a delete won't complain if there is nothing to delete.