问题描述
我有两个桌子:
1)区域2)地图
每个区域应至少具有1个地图，但也可以具有多个地图.
Each Area shall have at least 1 Map, but can also have more than one Map.
一张地图只能属于一个区域.
One Map can only belong to one Area.
如何在MySQL中构建它?
How to build this in MySQL?
推荐答案
在映射中添加引用区域主键的外键.这将在地图"和区域"之间建立一对多关系.
Add a Foreign key in Map that references the Area's Primary Key. That will enforce a one-to-many relationship between Maps and Areas.
关于在每个区域至少执行一张地图(如果有必要)，这篇文章中有一些想法在这里.一种更简单的解决方案是创建一个仅显示具有地图区域的视图:
As for enforcing a minimum of one map per area (if that is necessary) there are some ideas in this post here. One of the simpler solutions would be to create a view that only displays areas which have maps:
CREATE VIEW viewAreas AS
SELECT *
FROM Areas, Maps
WHERE Areas.ID = Maps.AreaID;
这样，您可以创建一个区域，然后向其添加地图.您还可以将地图中的外键强制为NOT NULL，因此地图必须始终具有一个区域.
This way, you can create an area, and then add maps to it. You can also enforce the Foreign Key in maps to be NOT NULL, so a map must always have an area.
这篇关于MySQL中的一对多关系-如何建立模型?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！