将外键添加到现有表中会出现错误1050表

Question

我有一个包含列的表CustomizationSet:

customization_set_guid (which is a non-nullable guid and also the primary key)
creator_account_guid
and a few others

和包含现有数据的表注册列:

registration_id (an int and the primary key)
customization_set_guid (also a guid (so a char(36)) which is nullable, and all entries are currently null)
and a few other columns

当我试着跑

ALTER TABLE Registration ADD FOREIGN KEY 
    (
        customization_set_guid
    ) REFERENCES CustomizationSet (
        customization_set_guid
    );

在MySQL Workbench中,它给出了错误1050Table'.\ dbname\registration'已经存在.

如果我尝试使用UI使用Alter Table对话框的Foreign Keys选项卡添加外键,并选择CustomizationSet作为引用表,则不允许我在列列表中选择customization_set_guid.

我真的不确定为什么它不会让我添加这个外键.我刚刚在我刚刚添加的表之间成功创建了外键.注册表已经存在了一段时间......

Answer 1

我得到了同样的错误,这是因为外键已经存在.你想要的只是添加约束:

ALTER TABLE Registration 
  ADD CONSTRAINT idx_Registration_CustomizationSet 
  FOREIGN KEY (customization_set_guid) 
  REFERENCES CustomizationSet(customization_set_guid);

Answer 2

所以一个团队成员想出了这个办法。其中一个表设置为 utf8_general 类型，另一个表设置为默认类型。我不认为这是一个问题，因为默认值是 utf8_general，但显然 mysql 只查看类型名称而不是底层类型。