Implement automatic numbering in sql server

There are two ways to implement automatic numbering in SQL Server: 1. Identify the data type and automatically generate a unique incremental value; 2. Sequence objects generate a unique incremental integer sequence. The selection method depends on the requirement: the identification is simple and easy to use, but resets the sequence when truncating or rebuilding the table; the sequence provides more granular control, but more complex to create and manage.

Implement automatic numbering in SQL Server

Automatic numbering is a database technology that allows the database to automatically generate unique sequences of numbers. In SQL Server, there are two main methods that can be used to implement automatic numbering:

1. Identity

• Identifying the data type automatically generates a unique value when a new row is inserted.
• The value is incremented (starting at 1) and is not repeated.

Example:

 <code class="sql">CREATE TABLE Customers ( CustomerID int IDENTITY(1, 1) PRIMARY KEY, FirstName varchar(50) NOT NULL, LastName varchar(50) NOT NULL );</code>

When a new row is inserted, CustomerID column's value will be automatically filled to 1, 2, 3, etc., and so on.

2. Sequence

• A sequence is an object that generates a unique and incremental sequence of integers.
• Sequences can be created and managed manually.

Example:

 <code class="sql">CREATE SEQUENCE CustomerSequence START WITH 1 INCREMENT BY 1; CREATE TABLE Customers ( CustomerID int PRIMARY KEY, FirstName varchar(50) NOT NULL, LastName varchar(50) NOT NULL ); ALTER TABLE Customers ADD CONSTRAINT DF_Customer_CustomerID DEFAULT (NEXT VALUE FOR CustomerSequence);</code>

When a new row is inserted, the value of CustomerID column will be automatically filled with the next value of the sequence (for example, 1, 2, 3, etc.).

Select method

Both identification and sequence can be used to implement automatic numbering, but they each have their advantages and disadvantages:

• Identification: Easy to use, but if the table is truncated or re-established, the sequence will be reset to 1.
• Sequence: allows for better control of sequence values, but is more complex to create and manage.

For simple cases, logos are usually a good choice. For situations where more advanced control is required, the sequence is more appropriate.

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