How to Add Identity Column to Table Based on Order of Another Column

How to Add Identity Column to Table Based on Order of Another Column

USE tempdb

GO
-- Create Table
CREATE TABLE TestTable (Col1 INT, Col2 VARCHAR(100))
GO
-- Insert Data
INSERT INTO TestTable (Col1, Col2)
VALUES (33, 'Ranjan');
INSERT INTO TestTable (Col1, Col2)
VALUES (22, 'shyam');
INSERT INTO TestTable (Col1, Col2)
VALUES (11, 'Tester');
GO
-- Select Data
SELECT *
FROM TestTable
GO
-- Add Identity Column
ALTER TABLE TestTable
ADD ID INT IDENTITY(1, 1)
GO
-- Select Data
SELECT *
FROM TestTable
GO
-- Clean up
DROP TABLE TestTable
GO

OR

USE tempdb

GO
-- Create Table
CREATE TABLE TestTable (Col1 INT, Col2 VARCHAR(100))
GO
-- Insert Data
INSERT INTO TestTable (Col1, Col2)
VALUES (33, 'Ranjan');
INSERT INTO TestTable (Col1, Col2)
VALUES (22, 'Shyam');
INSERT INTO TestTable (Col1, Col2)
VALUES (11, 'Tester');
GO
-- Select Data
SELECT *
FROM TestTable
GO
-- Create Clustered Index on Column ID
CREATE CLUSTERED INDEX IX_TestTable ON dbo.TestTable
(Col1 ASC)
GO
-- Add Identity Column
ALTER TABLE TestTable
ADD ID INT IDENTITY(1, 1)
GO
-- Select Data
SELECT *
FROM TestTable
GO
-- Clean up
DROP TABLE TestTable
GO

Is there any workaround to do the same?”

I quickly created clustered index in ASC order on Col1 and it ordered the table as expected and later added the identity column there. Let us see the script to get the desired result.

Here is one more idea:

Step1 – Create temporary clustered index on “date time column in descending order”

CREATE CLUSTERED INDEX ix_YourTableTEMP ON YourTable (DateTimeColumn DESC)

Step2 – Add identity column. Now the IDs should be in order of previously created index – although I don’t think there is 100% guarantee on this.

ALTER TABLE YourTable ADD IdColumn INT IDENTITY(1,1)

Step3 – Drop temporary index

DROP INDEX ix_YourTableTEMP ON YourTable

Step4 – Create new clustered PK on new column

ALTER TABLE YourTable
ADD CONSTRAINT PK_YourTable PRIMARY KEY CLUSTERED (IdColumn)