A foreign key relationship allows for the declaration of an index in one table to be related to an index in another. It also allows for the placing of constraints on what may be done to the tables in the relationship. The database enforces the rules of this relationship to maintain referential integrity. Using Foreign Keys with InnoDB The InnoDB storage engine supports the use of foreign keys (unlike other storage engines). This capability enables the declaration of relationships between columns in different tables, and InnoDB maintains integrity between the tables by prohibiting operations that violate those relationships. For example, the following restrictions must be addressed: • A table must contain only records with ID values that are known in another reference table. • If an ID in the referenced table is changed, the ID in all matching records in the referencing table must be changed to match. • If a record with a given ID in the referenced t
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