计算具有 3 个列值相同的行的出现次数 MySQL

Question

MySQL BEFORE INSERT 触发器

我有一个bookingstable。我有 3 列名为

facility_id, booking_date, time_slot

我还有另一个名为 facility 的 table，其中有一列名为 facility_id。它们由 WHERE bookings.faciliy_id = facility.facility_id

链接

我正在尝试计算预订 table 中的 3 列重复出现的次数，即：

1, 2017-02-02,08:00
1, 2017-02-02,08:00

我希望这是 2。

然后我试图检查这个结果，看看它是否 >= 到存储在设施 table 中的 facility_capacity。如果为真，则抛出错误消息。

DELIMITER
//
 CREATE TRIGGER facility_full BEFORE INSERT ON bookings
    FOR EACH ROW
        BEGIN 
        SELECT DISTINCT facility_id, booking_date, timeslot, COUNT(*) FROM bookings 
        SET COUNT = Answer
            IF (Answer) >=  facility_capacity
            THEN  SIGNAL SQLSTATE '45000' SET MESSAGE_TEXT = 'Facility Full';
            WHERE bookings.facility_id = facility.facility_id;
            END IF;
    END 
 //
 DELIMITER ;

Answer 1

如您所说，计算预订 table 中的 3 列重复出现的次数。这是解决您问题的一种方法。

DELIMITER
//
 CREATE TRIGGER facility_full BEFORE INSERT ON bookings
    FOR EACH ROW
        BEGIN 
        DECLARE v_count int;
        Declare msg TEXT;
        DECLARE v_facility_capacity  int;


        select count(*) into v_count from bookings where facility_id = New.facility_id and booking_date  = new.booking_date  and time_slot = new.time_slot;

select facility_capacity  into v_facility_capacity from facility 
where facility.facility_id = New.facility_id;

            IF (v_count) >=  v_facility_capacity  THEN
            set msg = concat('MyTriggerError: Facility Full: ', cast(new.facility_id as char));
            signal sqlstate '45000' set message_text = msg;
            END IF;
    END 
 //
 DELIMITER ;

计算具有 3 个列值相同的行的出现次数 MySQL

Counting occurrences of rows that have 3 column values the same MySQL

mysql

triggers

count

where

sql-insert