How to change an existing column to auto-increment column in SQL Server

In SQL server when you want to make an existing column to be auto-incremented.

The following code is not working:

ALTER TABLE [dwh].[ExchangeRate]
ALTER COLUMN [ExchangeRateId] Int Identity(1, 1)

What you could do is :

  • Create a new column with auto-increment
  • Delete existing column constraint
  • Delete the existing column
  • Rename the new column back
  • Add deleted constraint


Step 1: Create a new column

ALTER TABLE [dwh].[ExchangeRate]
ADD [ExchangeRateId2] Int Identity(1, 1)

Step 2: Delete existing constraint

ALTER TABLE [dwh].[ExchangeRate]
DROP CONSTRAINT [IxExchangeRate_ExchangeRateId_U_NC_]

Step 3: Delete existing column

ALTER TABLE [dwh].[ExchangeRate]
DROP COLUMN [ExchangeRateId]

Step 4: Rename new column

Exec sp_rename 'dwh.ExchangeRate.ExchangeRateId2', 'ExchangeRateId','COLUMN'

Step 5: Add deleted contraint

ALTER TABLE [dwh].[ExchangeRate] ADD  CONSTRAINT [IxExchangeRate_ExchangeRateId_U_NC_] PRIMARY KEY CLUSTERED 
(
[ExchangeRateId] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, SORT_IN_TEMPDB = OFF, IGNORE_DUP_KEY = OFF, ONLINE = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON, FILLFACTOR = 90) ON [PRIMARY]

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