Cannot create relationships to enforce referential integrity. Existing data in table <name> violates referential integrity rules in table <name>. (Error 3379)
You are trying to create a relationship using the CONSTRAINT clause of the ALTER TABLE statement, but existing data in the two tables violates referential integrity constraints. For example, there might be records relating to an employee in the related table but no corresponding record for the employee in the primary table.
To create the relationship, you must edit the data so that primary records exist for all related records.