In database design, primary key and foreign key are important concepts used to establish relationships between tables.
Primary Key:
- A primary key is a field used to uniquely identify each row in a table. The primary key must guarantee uniqueness and non-nullness, that is, the primary key value of each record must be unique and not empty.
Typically, the primary key is a separate field, and commonly used data types include integers (such as INT or BIGINT) or globally unique identifiers (GUIDs). Foreign key (Foreign
Key): - Foreign keys are used to establish relationships between tables and point to the primary key of another table.
The value stored by the foreign key field must exist in the primary key of the referenced table, or be NULL if allowed. In this way, foreign keys ensure data consistency and integrity between tables.
Foreign key fields are often used to represent relationships between tables, for example, an orders table may have a foreign key pointing to the primary key of the customer table, representing the relationship between orders and customers. Determine the primary key and foreign
The key steps are as follows:
primary key:
- Choose a field or set of fields as the primary key, ensuring its uniqueness and non-nullability. A common choice is to use an auto-incrementing integer as the primary key, for example using an auto-incrementing field of type INT.
foreign key:
- Identify the two tables that need to be associated, and choose a field as the foreign key, usually the primary key pointing to the other table.
When creating a foreign key, ensure that the data type and length of the foreign key field match the primary key of the referenced table.
When using foreign keys, consider referential integrity and ensure that the value of the foreign key field exists in the primary key of the referenced table.
Proper use of primary and foreign keys can help ensure data integrity and consistency of your databaseÿ