Primary key is a single or multiple fields (columns) in a database table that uniquely identify each record in the table. A primary key cannot contain null values.
Foreign key is a single or multiple fields (columns) in a database table that contain a reference to a field or fields of the primary key in another table. A foreign key is used to link tables together.
A primary key is typically used to identify records in a table. For example, in a table of "Books", the primary key could be the "Book ID" field. This field has a unique value for each record in the table, so it can be used to uniquely identify a book.
A foreign key is used to link tables together. For example, in a table of "Orders", the foreign key could be the "Book Code" field. This field contains the value of the primary key from the "Books" table. Thus, the foreign key can be used to link a record in the "Orders" table to the corresponding record in the "Books" table.
Primary and foreign keys are important elements of relational databases. They help to maintain data integrity and ensure the proper functioning of the database.
