What is an auto incremented key?

An auto-incremented key, also known as an identity key or serial key, is a type of column in a database table that is automatically assigned a unique numerical value whenever a new row is added to the table. The uniqueness of the auto-incremented key value ensures that each row in the table has its own distinct identifier. This is particularly useful for primary key columns, which uniquely identify each row and are often used as references in foreign key relationships between tables.

Auto-incremented keys are often used as primary keys because they provide a simple and efficient way to maintain the uniqueness of rows. They are also commonly used when there is a need for a system-generated, sequential, or unique identifier for each row in a table.

The way auto-incremented keys are implemented may vary depending on the specific database system. In some cases, the auto-incremented values may be generated using sequences, while in others, they may be managed directly by the database engine using a mechanism known as "identity columns" (in Microsoft SQL Server) or "serial columns" (in PostgreSQL).

Here's a simplified example of how an auto-incremented key might be used:

```sql

CREATE TABLE students (

student_id INT PRIMARY KEY AUTO_INCREMENT,

name VARCHAR(255) NOT NULL

);

```

In this example, the `student_id` column is defined as a primary key with the `AUTO_INCREMENT` keyword, which instructs the database to automatically generate a unique integer value for each new row added to the `students` table. As new students are added, their records will have a unique `student_id` assigned to them.

Auto-incremented keys are a common feature in most relational database management systems and are essential for maintaining referential integrity and creating efficient table structures.