MySQL Primary Key and Foreign Key: Establishing Table Relationships in Simple Terms for Beginners

This article explains the necessity of primary keys and foreign keys for database orderliness. A primary key is a field within a table that uniquely identifies data (e.g., `class_id` in a class table), ensuring data uniqueness and non-nullability, similar to an "ID card." A foreign key is a field in a child table that references the primary key of a parent table (e.g., `class_id` in a student table), establishing relationships between tables and preventing invalid child table data (e.g., a student belonging to a non-existent class). The core table relationship is **one-to-many**: a class table (parent table) corresponds to multiple student records (child table), with the foreign key dependent on the existence of the parent table's primary key. Key considerations: foreign keys must have the same data type as primary keys, the InnoDB engine must be used, and data in the parent table must be inserted first. Summary: Primary keys ensure data uniqueness within a table, while foreign keys maintain relationships between tables. In a one-to-many relationship, the parent table's primary key and the child table's foreign key are central, resulting in a clear and efficient database structure.