Forgot to add primary key column as Identity - sql

Question

I had created a table like this
CREATE TABLE [dbo].[sydShopOrder](
[rowNumber] [varchar](50) NULL,
[firstName] [varchar](50) NULL,
[lastName] [varchar](50) NULL,
[employeeNumber] [varchar](50) NULL,
[productID] [varchar](50) NULL,
[shopID] [varchar](50) NULL,
[location] [varchar](50) NULL,
[address] [varchar](50) NULL,
[department] [varchar](50) NULL,
[datestamp] [date] NULL
) ON [PRIMARY]
I was intended to make [rowNumber] as primary key and make it identity column with auto increment. But I forgot to do it. And now the database is up and running in live environment. I had found this bug very late. Is there any way that I can fix this? Make [rowNumber] column as identity and auto increment it?
Current screenshot of table looks like this

Answer 1

You can drop [rownumber] and then add with identity
Alter Table [dbo].[sydShopOrder] Drop Column rownumber
Go
Alter Table [dbo].[sydShopOrder]
Add rownumber Int Identity(1, 1)
Go
If you want to populate the identity field for existing data, better to create another temporary table, and keep all the records of [dbo].[sydShopOrder] in that. After that truncate [dbo].[sydShopOrder] and then insert the values from that temp table to [dbo].[sydShopOrder]
CREATE TABLE #temp ([firstName] [varchar](50) NULL,
[lastName] [varchar](50) NULL,
[employeeNumber] [varchar](50) NULL,
[productID] [varchar](50) NULL,
[shopID] [varchar](50) NULL,
[location] [varchar](50) NULL,
[address] [varchar](50) NULL,
[department] [varchar](50) NULL,
[datestamp] [date] NULL)
INSERT INTO #temp
SELECT [firstName],[lastName],[employeeNumber],
[productID], [shopID],[location],
[address],[department],[datestamp]
FROM [dbo].[sydShopOrder]
TRUNCATE TABLE [dbo].[sydShopOrder]
INSERT INTO [dbo].[sydShopOrder]
SELECT * FROM #temp
Here is a sample SQLFIDDLE