Question

我有两张桌子：会谈和日子。会谈看起来像：

+----+----------------------------------+--------+
| Id |               Name               | Leader |
+----+----------------------------------+--------+
|  1 | How to improve revenue for tacos | Tacob  |
|  2 | Improving sales potential        | Bocat  |
+----+----------------------------------+--------+

和日子：

+--------+-----+
| TalkId | Day |
+--------+-----+
|      1 | Mon |
|      1 | Tue |
|      1 | Thu |
|      2 | Mon |
|      2 | Tue |
+--------+-----+

TalkId是引用Talks表的外键。

外键强制执行＆＃34; A Day需要Talk＆＃34;的关系。但是，我还想强制执行相反的关系＆＃34;谈话需要至少一天＆＃34;。

我知道这个约束类似于多对多关系，两个记录都相互依赖。但是，在这种情况下，很多天引用一个讲话，但只有一个讲话引用很多天。

另一个问题是，在创建这样的约束之后，如何一次插入两个记录？

我已经搜索了其他问题，但只找到了多对多关系的案例，结果如下：

+----+----------------------------------+--------+
| Id |               Name               | Leader |
+----+----------------------------------+--------+
|  1 | How to improve revenue for tacos | Tacob  |
|  2 | Improving sales potential        | Bocat  |
+----+----------------------------------+--------+

+----+-----+
| Id | Day |
+----+-----+
|  1 | Mon |
|  2 | Tue |
|  3 | Thu |
|  4 | Mon |
|  5 | Tue |
+----+-----+

+--------+-------+
| TalkId | DayId |
+--------+-------+
|      1 |     1 |
|      1 |     2 |
|      1 |     3 |
|      2 |     4 |
|      2 |     5 |
+--------+-------+

其中TalkId引用Talks Id和DayId引用Days＆＃39; s Id。

修改：

忽略我上面要求的内容。

我希望能够做到：

SELECT全部有效Talks
SELECT全部有效Days

我希望无法做到：

INSERT Talk没有Day
INSERT Day没有Talk

Answer 1

听起来你想要一个简单的外键关系：

alter table days add constraint fk_days_talkid foreign key (talkid) references talks(talkid);

这可以保证talkid有效。然后，您将days.talkid声明为not null，并保证您描述的关系。

Answer 2

-- Day named (TheDay) exists.
--
Calendar {TheDay}
      PK {TheDay}


-- Talk (TalkID) titled (TalkName), presented by (Leader) is by default
-- scheduled on (DefaultDay).

Talk {TalkID, TalkName, Leader, DefaultDay}
  PK {TalkID}
  AK {TalkName}

FOREIGN KEY {DefaultDay} REFERENCES Calendar {TheDay}


--Talk (TalkID) is also scheduled on (TheDay).
--
TalkDay {TalkID, TheDay}
     PK {TalkID, TheDay}

FOREIGN KEY {TalkID} REFERENCES Talk     {TalkID}
FOREIGN KEY {TheDay} REFERENCES Calendar {TheDay}

Note PK = primary key
     AK = alternate key (unique)
     All attributes (columns) NOT NULL

选择特定演讲的所有日期：

select TalkName, DefaultDay as TalkDay
from Talk
where TalkName = 'How to improve revenue for tacos'

union

select TalkName, b.TheDay as TalkDay
from Talk    as a
join TalkDay as b on b.TalkID = a.TalkID
where a.TalkName = 'How to improve revenue for tacos'

选择特定日期的所有讲座：

select TalkName, DefaultDay as TalkDay
from Talk
where DefaultDay = 'Tue'

union

select TalkName, b.TheDay as TalkDay
from Talk    as a
join TalkDay as b on b.TalkID = a.TalkID
where b.TheDay = 'Tue'

多表与表记录需要彼此

2 个答案: