Question

我有两个桌子；

tbl_ride

+---------+--------------+----------+
| rideID  |   rideName   | duration |
+---------+--------------+----------+
|   1     |    NY Tour   |     3    |
|   2     | Night Life   |     2    |
+---------+--------------+----------+

tbl_day

+------------+-----------+----------+
| dayID      |   rideID  | routeMap |
+---------+--------------+----------+
|   1        |     1     |   A-B    |
|   2        |     1     |   B-C    |
|   3        |     1     |   C-D    |
|   4        |     2     |   A-B    |
|   5        |     2     |   B-C    |
+---------+--------------+----------+

所以我需要能够基于tbl_day限制记录到tbl_ride.duration中的记录数。可以通过SQL来实现还是应该通过代码来实现？无论哪种方式，我都会感谢您的帮助。

以下是我当前用于JDBC的MySQL代码：

INSERT INTO `tbl_tour_day` (`tourID`, `startHotel`, `endHotel`, `routeNote`, `routeMap`) 
VALUES ( (SELECT tourID from tbl_tour_ride where tbl_tour_ride.tourID = ?), ?, ?, ?, ?)

Answer 1

以下是有效查询的示例：

INSERT INTO tbl_tour_day 
(tourID
,startHotel
,endHotel
,routeNote
,routeMap
)  
SELECT tourID 
     , ?
     , ?
     , ?
     , ?
  from tbl_tour_ride 
 where tbl_tour_ride.tourID = ?

Answer 2

测试

CREATE TRIGGER tr_bi_tbl_day
BEFORE INSERT 
ON tbl_day
FOR EACH ROW
BEGIN
IF    COALESCE(( SELECT COUNT(*) FROM tbl_day WHERE rideID = NEW.rideID ), 0)
   >=
      COALESCE(( SELECT MAX(duration) FROM tbl_ride WHERE rideID = NEW.rideID ), 0) THEN
    SIGNAL SQLSTATE = '45000' 
        SET MESSAGE_TEXT = 'All days for this ride has been specified';
END IF;
END

如果在tbl_ride中没有新rideID的记录，则不允许插入（假定为零）。

如果tbl_ride中有多个新rideID记录，则将最大值用作限制。

如何根据外键值限制“插入”？

2 个答案: