Turning IDENTITY_INSERT On and Off in SQL Server 2008

Turning IDENTITY_INSERT On and Off in SQL Server 2008

Understanding IDENTITY_INSERT

In SQL Server 2008, the IDENTITY property of a column automatically assigns a unique, sequential number to each new row inserted into the table. This is often used for primary key columns. However, there might be situations where you need to manually specify the value for an IDENTITY column, such as when importing data from another system.

Turning IDENTITY_INSERT On

To temporarily override the automatic IDENTITY generation and allow you to manually specify values for an IDENTITY column, you use the SET IDENTITY_INSERT statement. Here's the syntax:

SET IDENTITY_INSERT [schema_name].[table_name] ON;

Replace [schema_name].[table_name] with the actual name of your table.

Example:

SET IDENTITY_INSERT dbo.Customers ON;

This enables you to insert rows into the Customers table, specifying the value for the CustomerID column.

Inserting Rows with Manually Specified Values Once IDENTITY_INSERT is turned on, you can insert rows using the INSERT statement, specifying the value for the IDENTITY column:

INSERT INTO dbo.Customers (CustomerID, CustomerName, ...)
VALUES (1000, 'John Doe', ...);

Turning IDENTITY_INSERT Off After you've finished inserting rows with manually specified values, you should turn off IDENTITY_INSERT to resume automatic generation:

SET IDENTITY_INSERT [schema_name].[table_name] OFF;

SET IDENTITY_INSERT dbo.Customers OFF;

Important Considerations:

• Scoped to the Table: The SET IDENTITY_INSERT statement applies only to the specified table.
• Temporary: The setting is temporary and is reset when the connection is closed.
• Potential Data Integrity Issues: If you're not careful, turning off IDENTITY_INSERT without inserting the correct IDENTITY values can lead to data integrity issues.

Use Cases:

• Data Migration: When importing data from a system that doesn't use IDENTITY columns.
• Testing and Debugging: For testing purposes or to correct data errors.

Creating a Sample Table

Let's first create a sample table with an IDENTITY column:

CREATE TABLE Customers (
    CustomerID INT IDENTITY(1,1) PRIMARY KEY,
    CustomerName VARCHAR(50)
);

Turning IDENTITY_INSERT On and Inserting a Row

SET IDENTITY_INSERT dbo.Customers ON;

INSERT INTO dbo.Customers (CustomerID, CustomerName)
VALUES (1001, 'John Doe');

SET IDENTITY_INSERT dbo.Customers OFF;

In this example:

1. We enable IDENTITY_INSERT for the Customers table.
2. We insert a row with a manually specified CustomerID of 1001.
3. We disable IDENTITY_INSERT to resume automatic generation.

SET IDENTITY_INSERT dbo.Customers ON;

INSERT INTO dbo.Customers (CustomerID, CustomerName)
VALUES
    (1002, 'Jane Smith'),
    (1003, 'Michael Johnson');

SET IDENTITY_INSERT dbo.Customers OFF;

Here, we insert multiple rows with manually specified CustomerID values in a single INSERT statement.

Turning IDENTITY_INSERT On and Inserting Rows from a Temporary Table

-- Create a temporary table
CREATE TABLE #TempCustomers (
    CustomerID INT,
    CustomerName VARCHAR(50)
);

-- Insert data into the temporary table
INSERT INTO #TempCustomers (CustomerID, CustomerName)
VALUES
    (1004, 'Emily Davis'),
    (1005, 'David Lee');

-- Turn on IDENTITY_INSERT and insert rows from the temporary table
SET IDENTITY_INSERT dbo.Customers ON;

INSERT INTO dbo.Customers (CustomerID, CustomerName)
SELECT CustomerID, CustomerName
FROM #TempCustomers;

SET IDENTITY_INSERT dbo.Customers OFF;

-- Drop the temporary table
DROP TABLE #TempCustomers;

In this example, we use a temporary table to store the data before inserting it into the main table with IDENTITY_INSERT enabled.

Using a Sequence Object

• Introduction: SQL Server 2012 introduced sequence objects, which provide a more flexible and efficient way to generate sequential numbers.
• Steps:
  1. Create a sequence object:

     CREATE SEQUENCE dbo.MySequence
     START WITH 1
     INCREMENT BY 1
     CACHE 1000
     MINVALUE 1
     MAXVALUE 2147483647;
     

  2. Use the sequence in your INSERT statements:

     INSERT INTO dbo.Customers (CustomerID, CustomerName)
     VALUES (NEXT VALUE FOR dbo.MySequence, 'New Customer');
     

Using a Trigger

• Introduction: A trigger can be used to intercept INSERT statements and assign a specific value to the IDENTITY column.
• Steps:
  1. Insert data into the table as usual.

Using a Stored Procedure

• Introduction: A stored procedure can encapsulate the logic for assigning values to the IDENTITY column.
• Steps:
  1. Call the stored procedure to insert data:

     EXEC sp_InsertCustomer 'New Customer';
     

Choosing the Right Method:

• Sequence Objects: Generally preferred for their flexibility, efficiency, and scalability.
• Triggers: Useful when you need to perform additional actions before or after inserting data.
• Stored Procedures: Can provide a more encapsulated and reusable approach.