foreign key constraint

foreign key constraint
What is a foreign key constraint? Why are such constraints important? What is referential integrity?
Consider the ER diagram that you designed for the Prescriptions-R-X chain of pharmacies. Dene relations corresponding to the entity sets and relationship sets in your design using SQL.
Write SQL statements to create the corresponding relations to the ER diagram you designed. If your translation cannot capture any constraints in the ER diagram, explain why.
foreign key constraint