Referential integrity

 🔴Every foreign key value has a matching value in the corresponding primary key
🔵Referential integrity uses these to prevent the deletion of related records
🔴It can alert if the user tries to delete a record which is related to another one
🔵Queries will begin to fail if the relationships do not match
🔴If a table is relying on the keys in another table, then relationships between the two can be lost if bad data is entered into one location
🔵Referential integrity can be used to ensure foreign key values are valid. 
🔴Prevents the entry of duplicate data
🔵Prevents records being added to a related table if there is no associated
record in the primary table
🔴Prevents the changing of values in a primary table that result in orphaned
records in a related table
🔵Prevents the deletion of records from a primary table if there are matching
related records.