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Sequence object in SQL Server

In SQL Server, a Sequence object is a user-defined database object that generates a sequence of numeric values in a specified range. It is often used to generate unique identifiers for tables or other purposes where a sequential numeric value is required.

Sequences were introduced in SQL Server 2012 as a new feature to provide an alternative to the traditional identity columns. Unlike identity columns, sequences are not associated with a specific table, allowing them to be shared across multiple tables or even multiple databases.

Here's an example of how to create and use a sequence object in SQL Server:

1- Creating a Sequence:


CREATE SEQUENCE MySequence
    START WITH 1
    INCREMENT BY 1
    MINVALUE 1
    MAXVALUE 1000
    CYCLE;

In this example, we create a sequence called "MySequence" that starts at 1 and increments by 1. The sequence will generate values between 1 and 1000. The CYCLE option means that when the maximum value is reached, the sequence will restart from the minimum value.

2- Using a Sequence:


-- Retrieve the next value from the sequence
DECLARE @NextValue INT;
SET @NextValue = NEXT VALUE FOR MySequence;
SELECT @NextValue;

-- Using the sequence in a table
CREATE TABLE MyTable (
    ID INT PRIMARY KEY,
    Name VARCHAR(50)
);

INSERT INTO MyTable (ID, Name)
VALUES (NEXT VALUE FOR MySequence, 'John Doe');

In this example, we retrieve the next value from the sequence using the NEXT VALUE FOR syntax and store it in a variable. We can then use the variable as needed. We also demonstrate how to use the sequence to generate a unique identifier for the ID column in a table.

Sequences provide more flexibility compared to identity columns, as they allow you to generate sequential values outside of a table's insert operation. They can be useful in scenarios where you need to control the generation of unique identifiers manually or when you need to generate sequential values for other purposes.

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