autoincrementIDENTITY

autoincrementIDENTITY is a database feature that automatically generates a unique numeric value for each new row in a table. It is commonly used for primary keys to ensure that every record can be uniquely identified without manual input. Although the general concept is consistent, the exact syntax and behavior differ between database systems.

In SQL Server, autoincrement is implemented with the IDENTITY property on a column, often defined as IDENTITY(seed, increment) to specify the starting value and step. In MySQL, the equivalent feature is AUTO_INCREMENT on a column, and the value can be automatically increased with insert operations. PostgreSQL historically used sequences and the SERIAL type, but newer standards offer GENERATED ALWAYS AS IDENTITY or GENERATED BY DEFAULT AS IDENTITY as standard-compliant options. Other databases may implement their own variants with internal sequences or auto-increment counters.

From a design perspective, identity columns are typically used for primary keys and are designed to be unique and non-null. The values are usually monotone increasing, though some systems allow gaps when transactions roll back or rows are deleted. The implementation can be backed by a separate sequence object or by an internal counter, and, in some cases, caching can affect how many values are generated in advance for performance.

Administrators should consider potential wraparound limits, the impact of reseeding, and whether to expose generated values to applications. Identity columns should be used solely for identification keys rather than encoding business logic. They interact with foreign keys and can complicate replication or sharding if the value ranges need coordination.