SQL Server IDENTITY vs SEQUENCE: How to Pick the Right Auto-Increment Strategy

SQL Server offers two auto-increment mechanisms — IDENTITY and SEQUENCE — each suited to different use cases. IDENTITY is a column-level property ideal for simple, single-table surrogate keys, while SEQUENCE is a standalone database object that can be shared across multiple tables and supports advanced options like CACHE, CYCLE, and value pre-allocation. A real-world cautionary example shows a logistics system's INT IDENTITY column hitting its maximum integer limit of 2,147,483,647 after three years, causing insert failures and requiring an emergency migration of 900 million rows. Neither mechanism guarantees gapless numbering, as rollbacks, restarts, and cache flushes all cause values to be skipped permanently. Portability is another distinction: SEQUENCE follows the ANSI SQL standard and is supported by PostgreSQL, Oracle, and Db2, whereas IDENTITY is specific to SQL Server.