Looking through a database, I came across a table that used its primary key as a foreign key to itself.
I've seen that a table can have a foreign key to itself to build a hierarchy structure, but it would use another column to reference the primary key.
Since the primary key is unique, in this situation wouldn't the row only be able to point back to itself? That seems to be a tautological link, since if I already have the row, then I already have the row.
Is there any reason this would be done?
I am certain the constraint is written that way (not just looking at the diagram) because the same table and column are used for both halves of the definition.