How to Alter Sequence in SQL Server

In SQL Server, a sequence is a user-defined object that generates a sequence of numeric values in a specified order. Sequences are used to generate unique numbers for various database applications such as generating primary key values. At times, you may need to modify the properties of a sequence. Here's how you can alter a sequence in SQL Server.

Step 1: Check the Current Sequence Properties

Before making any changes, you should first examine the current properties of the sequence. You can do this by using the following query:

SELECT * 
FROM sys.sequences
WHERE name = 'YourSequenceName';
                                

Step 2: Alter the Sequence

To alter the sequence, use the ALTER SEQUENCE statement. The ALTER SEQUENCE statement allows you to modify properties such as increment, start value, or cycle option. Here's a basic example:

ALTER SEQUENCE YourSequenceName
    RESTART WITH 1000;
                                

This command restarts the sequence at 1000. You can also change the increment or other properties as needed. Here's an example to change the increment:

ALTER SEQUENCE YourSequenceName
    INCREMENT BY 5;
                                

Step 3: Set Sequence to Cycle

To make a sequence cycle when it reaches its maximum or minimum value, use the CYCLE option:

ALTER SEQUENCE YourSequenceName
    CYCLE;
                                

Step 4: Remove the Cycle Option

If you no longer want the sequence to cycle, use the NO CYCLE option:

ALTER SEQUENCE YourSequenceName
    NO CYCLE;
                                

Important Notes

• Altering a sequence doesn't affect the existing values already generated by the sequence. You may want to manually adjust the sequence values if needed.
• When altering a sequence, ensure that no active transactions or objects are relying on the sequence to avoid conflicts.
• The RESTART option resets the sequence value, which may not always be desirable in a production environment.

Conclusion

Altering a sequence in SQL Server is straightforward using the ALTER SEQUENCE statement. This gives you flexibility in adjusting sequence properties as your application needs change. Always ensure that any changes you make are thoroughly tested, especially when working in production environments.