Missing Foreign Key

[andrewchiu198]

sqlalchemy.exc.OperationalError: (pymysql.err.OperationalError) (6125, "Failed to add the foreign key constraint. Missing unique key for constraint 'orbitfits_ibfk_1' in the referenced table 'Planets'")
[SQL: ALTER TABLE OrbitFits ADD FOREIGN KEY (pl_id) REFERENCES Planets(pl_id) ON DELETE NO ACTION ON UPDATE NO ACTION]

Return to original database schema,
work back in the commented out code.
line 2086 of plandb_methods