如何在 Mysql 工作台中创建零或一对多关系
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How to create a zero or one to many relationship in Mysql workbench
提问by Redaa
In a database that have Orders, Customers tables, i need the relation between these two tables to be zero or one to many relationship, simply because in my application, an order can exist without being assigned to a customer.
在具有订单、客户表的数据库中，我需要这两个表之间的关系为零或一对多关系，因为在我的应用程序中，订单可以存在而无需分配给客户。
One first idea that comes to my mind is to make the foreign key nullable, this way when creating an order the foreign key can be null, but i don't know how to do so. I'm working on a model so i can render it to my 'teacher', so i need to know how to do it using the EER diagram.
我想到的第一个想法是使外键可以为空，这样在创建订单时外键可以为空，但我不知道该怎么做。我正在研究一个模型，所以我可以将它呈现给我的“老师”，所以我需要知道如何使用 EER 图来做到这一点。
thanks in advance.
提前致谢。
采纳答案by K.A.F.
Create your 1:n relationship as normal. Then double click the table to bring up the details. On your new FK field, uncheck the "NN" column. Now your FK can be NULL.
像往常一样创建您的 1:n 关系。然后双击表格以显示详细信息。在新的 FK 字段上，取消选中“NN”列。现在您的 FK 可以为 NULL。
回答by gomi
Mandatory option in "Foreign Key" tab in "Relationship" tab appears to be the way to control optionality.
“关系”选项卡中“外键”选项卡中的强制选项似乎是控制可选性的方式。
