Understanding Azure SQL Database Sequences: A Beginner's Guide

What Are Azure SQL Database Sequences?

Database sequences in Azure SQL are user-defined schema-bound objects that generate a sequence of numeric values according to a specification. Unlike identity columns, sequences are independent of tables and can be used across multiple tables or columns.

Key Features

• Independent of tables: Sequences are not tied to any specific table.
• Reusable: The same sequence can supply values for multiple tables.
• Flexible: You can define starting value, increment, minimum, maximum, and cycling behavior.

Creating a Sequence

CREATE SEQUENCE dbo.OrderNumberSeq
    START WITH 1000
    INCREMENT BY 1
    MINVALUE 1000
    MAXVALUE 9999
    CYCLE;

Using a Sequence

INSERT INTO Orders (OrderID, Product, Quantity)
VALUES (NEXT VALUE FOR dbo.OrderNumberSeq, 'Widget', 5);

Benefits Over Identity Columns

• Share across tables: Multiple tables can use the same sequence.
• Gap control: You can retrieve the next value without inserting a row.
• Performance: Sequences can be cached to reduce I/O.

Best Practices

• Use sequences when you need unique numbers across multiple tables or when you need to know the value before insertion.
• Consider caching settings for high-volume scenarios.
• Always test for boundary conditions when cycling.

By mastering sequences, you can design more flexible and scalable database solutions in Azure SQL.