A database primary key must meet the following conditions:
Uniqueness: Each value in the primary key column must be unique across all rows in the table. This ensures that no two records can have the same primary key value, allowing for precise identification of each row.
Example: In a users table, the user_id column as a primary key must ensure that no two users share the same user_id.
Non-null (Not Null): The primary key column cannot contain NULL values. Every row must have a valid, non-null value in the primary key field to maintain data integrity.
Example: If order_id is the primary key in an orders table, every order must have a defined order_id; it cannot be left empty.
Immutable (Generally): While not always strictly enforced by all database systems, it is a best practice that the value of a primary key should not change over time. Changing a primary key can lead to complications with related data in foreign key relationships.
In relational databases, the primary key is often used to enforce entity integrity and establish relationships with other tables via foreign keys.
For managing databases where you need reliable primary key enforcement, services like TencentDB for MySQL, TencentDB for PostgreSQL, or Tencent Distributed SQL provide robust support for defining and maintaining primary keys with high availability and performance. These services ensure that your primary key constraints are properly enforced, helping maintain data consistency and integrity.