添加另一个名为 isactive 之类的列.在 (username, isactive) 上创建唯一约束.

Add another column called something like isactive. The create a unique constraint on (username, isactive).

然后您可以同时拥有活动和非活动用户名.您将无法拥有两个活动用户名.

Then you can have both an active and inactive user name at the same time. You will not be able to have two active user names.

如果您想要多个非活动名称，请使用 NULL 作为 isactive 的值.NULL 值可以在唯一索引中重复.

If you want multiple inactive names, use NULL for the value of isactive. NULL values can be repeated in a unique index.