添加自引用外键SQL Server时出错

Question

I have a table called User that has columns like:

|UserID numeric(18,0)
|...
|SupervisorUserID numeric(18,0)

UserID is the primary key and I have other foreign key relationships working (table to table). But when I try to add a relation between SupervisorUserID and UserID I get the following error in SQL Server Management Studio:

What could be the issue here?

Answer 1

The message looks quite straightforward. Check if your index is unique.

Answer 2

When you create a foreign key relationship in the same table make sure you put the primary key field under "Primary key table" and the foreign key field under "Foreign key table". Doing the reverse will give you the error described.