What is the difference between a primary key and a foreign key?

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## Primary Key vs. Foreign Key Primary keys and foreign keys define database constraints that guarantee relational integrity across tables: - **Primary Key (PK):** Uniquely identifies each record inside a table. It cannot contain `NULL` values, and a table can have **only one** primary key. - **Foreign Key (FK):** Reference column that maps to a primary key in another table (or the same table). It enforces **referential integrity**, ensuring that the value in the child column matches an existing parent row key.

What is the difference between a primary key and a foreign key?

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