Adding an identity to an existing column

I need to change the primary key of a table to an identity column, and there's already a number of rows in table.

I've got a script to clean up the IDs to ensure they're sequential starting at 1, works fine on my test database.

What's the SQL command to alter the column to have an identity property?

I don't believe you can alter an existing column to be an identity column using tsql. However, you can do it through the Enterprise Manager design view.

Alternatively you could create a new row as the identity column, drop the old column, then rename your new column.

ALTER TABLE FooTable
ADD BarColumn INT IDENTITY(1, 1)
NOT NULL
PRIMARY KEY CLUSTERED

There isn't one, sadly; the IDENTITY property belongs to the table rather than the column.

The easier way is to do it in the GUI, but if this isn't an option, you can go the long way around of copying the data, dropping the column, re-adding it with identity, and putting the data back.

See [here](

[To see links please register here]

) for a blow-by-blow account.

By design there is no simple way to turn on or turn off the identity feature for an existing column. The only clean way to do this is to create a new column and make it an identity column or create a new table and migrate your data.

If we use SQL Server Management Studio to get rid of the identity value on column "id", a new temporary table is created, the data is moved to the temporary table, the old table is dropped and the new table is renamed.

Use Management Studio to make the change and then right click in the designer and select "Generate Change Script".

You will see that this is what SQL server in doing in the background.

you can't do it like that, you need to add another column, drop the original column and rename the new column or or create a new table, copy the data in and drop the old table followed by renaming the new table to the old table

if you use SSMS and set the identity property to ON in the designer here is what SQL Server does behind the scenes. So if you have a table named [user] this is what happens if you make UserID and identity

BEGIN TRANSACTION
SET QUOTED_IDENTIFIER ON
SET TRANSACTION ISOLATION LEVEL SERIALIZABLE
SET ARITHABORT ON
SET NUMERIC_ROUNDABORT OFF
SET CONCAT_NULL_YIELDS_NULL ON
SET ANSI_NULLS ON
SET ANSI_PADDING ON
SET ANSI_WARNINGS ON
COMMIT
BEGIN TRANSACTION

GO

GO
CREATE TABLE dbo.Tmp_User
(
UserID int NOT NULL IDENTITY (1, 1),
LastName varchar(50) NOT NULL,
FirstName varchar(50) NOT NULL,
MiddleInitial char(1) NULL

) ON [PRIMARY]
GO

SET IDENTITY_INSERT dbo.Tmp_User ON
GO
IF EXISTS(SELECT * FROM dbo.[User])
EXEC('INSERT INTO dbo.Tmp_User (UserID, LastName, FirstName, MiddleInitial)
SELECT UserID, LastName, FirstName, MiddleInitialFROM dbo.[User] TABLOCKX')
GO
SET IDENTITY_INSERT dbo.Tmp_User OFF
GO

GO
DROP TABLE dbo.[User]
GO
EXECUTE sp_rename N'dbo.Tmp_User', N'User', 'OBJECT'
GO
ALTER TABLE dbo.[User] ADD CONSTRAINT
PK_User PRIMARY KEY CLUSTERED
(
UserID
) ON [PRIMARY]

GO
COMMIT



Having said that there is a way to hack the system table to accomplish it by setting the bitwise value but that is not supported and I wouldn't do it

If the original poster was actually wanting to set an existing column to be a `PRIMARY KEY` for the table and actually did not need the column to be an `IDENTITY` column (two different things) then this can be done via t-SQL with:

ALTER TABLE [YourTableName]
ADD CONSTRAINT [ColumnToSetAsPrimaryKey] PRIMARY KEY ([ColumnToSetAsPrimaryKey])

Note the parenthesis around the column name after the `PRIMARY KEY` option.

Although this post is old and I am making an assumption about the requestors need, I felt this additional information could be helpful to users encountering this thread as I believe the conversation could lead one to believe that an existing column can not be set to be a primary key without adding it as a new column first which would be incorrect.

There is cool solution described here:
[SQL SERVER – Add or Remove Identity Property on Column][1]

In short edit manually your table in SQL Manager, switch the identity, DO NOT SAVE changes, just show the script which will be created for the changes, copy it and use it later.

It is huge time saver, because it (the script) contains all the foreign keys, indices, etc. related to the table you change. Writting this manually... God forbid.


[1]:

[To see links please register here]

Basically there are four logical steps.

1. Create a new Identity column. Turn on Insert Identity for this new column.

2. Insert the data from the source column (the column you wished to convert to Identity) to this new column.

3. Turn off the Insert Identity for the new column.

4. Drop your source column & rename the new column to the name of the source column.

There may be some more complexities like working across multiple servers etc.

Please refer the following article for the steps (using ssms & T-sql). These steps are intended for beginners with less grip on T-SQL.

[

[To see links please register here]

][1]


[1]:

[To see links please register here]

generates a script for all tables with primary key = bigint which do not have an identity set; this will return a list of generated scripts with each table;

SET NOCOUNT ON;

declare @sql table(s varchar(max), id int identity)

DECLARE @table_name nvarchar(max),
@table_schema nvarchar(max);

DECLARE vendor_cursor CURSOR FOR
SELECT
t.name, s.name
FROM sys.schemas AS s
INNER JOIN sys.tables AS t
ON s.[schema_id] = t.[schema_id]
WHERE EXISTS (
SELECT
[c].[name]
from sys.columns [c]
join sys.types [y] on [y].system_type_id = [c].system_type_id
where [c].[object_id] = [t].[object_id] and [y].name = 'bigint' and [c].[column_id] = 1
) and NOT EXISTS
(
SELECT 1 FROM sys.identity_columns
WHERE [object_id] = t.[object_id]
) and exists (
select 1 from sys.indexes as [i]
inner join sys.index_columns as [ic] ON i.OBJECT_ID = ic.OBJECT_ID AND i.index_id = ic.index_id
where object_name([ic].[object_id]) = [t].[name]
)
OPEN vendor_cursor

FETCH NEXT FROM vendor_cursor
INTO @table_name, @table_schema

WHILE @@FETCH_STATUS = 0
BEGIN

DELETE FROM @sql

declare @pkname varchar(100),
@pkcol nvarchar(100)

SELECT top 1
@pkname = i.name,
@pkcol = COL_NAME(ic.OBJECT_ID,ic.column_id)
FROM sys.indexes AS [i]
INNER JOIN sys.index_columns AS [ic] ON i.OBJECT_ID = ic.OBJECT_ID AND i.index_id = ic.index_id
WHERE i.is_primary_key = 1 and OBJECT_NAME(ic.OBJECT_ID) = @table_name

declare @q nvarchar(max) = 'SELECT '+@pkcol+' FROM ['+@table_schema+'].['+@table_name+'] ORDER BY '+@pkcol+' DESC'

DECLARE @ident_seed nvarchar(max) -- Change this to the datatype that you are after
SET @q = REPLACE(@q, 'SELECT', 'SELECT TOP 1 @output = ')
EXEC sp_executeSql @q, N'@output bigint OUTPUT', @ident_seed OUTPUT

insert into @sql(s) values ('BEGIN TRANSACTION')
insert into @sql(s) values ('BEGIN TRY')

-- create statement
insert into @sql(s) values ('create table ['+@table_schema+'].[' + @table_name + '_Temp] (')

-- column list
insert into @sql(s)
select
' ['+[c].[name]+'] ' +
y.name +

(case when [y].[name] like '%varchar' then
coalesce('('+(case when ([c].[max_length] < 0 or [c].[max_length] >= 1024) then 'max' else cast([c].max_length as varchar) end)+')','')
else '' end)

+ ' ' +
case when [c].name = @pkcol then 'IDENTITY(' +COALESCE(@ident_seed, '1')+',1)' else '' end + ' ' +
( case when c.is_nullable = 0 then 'NOT ' else '' end ) + 'NULL ' +
coalesce('DEFAULT ('+(
REPLACE(
REPLACE(
LTrim(
RTrim(
REPLACE(
REPLACE(
REPLACE(
REPLACE(
LTrim(
RTrim(
REPLACE(
REPLACE(
object_definition([c].default_object_id)
,' ','~')
,')',' ')
)
)
,' ','*')
,'~',' ')
,' ','~')
,'(',' ')
)
)
,' ','*')
,'~',' ')
) +
case when object_definition([c].default_object_id) like '%get%date%' then '()' else '' end
+
')','') + ','
from sys.columns c
JOIN sys.types y ON y.system_type_id = c.system_type_id
where OBJECT_NAME(c.[object_id]) = @table_name and [y].name != 'sysname'
order by [c].column_id


update @sql set s=left(s,len(s)-1) where id=@@identity

-- closing bracket
insert into @sql(s) values( ')' )

insert into @sql(s) values( 'SET IDENTITY_INSERT ['+@table_schema+'].['+@table_name+'_Temp] ON')

declare @cols nvarchar(max)
SELECT @cols = STUFF(
(
select ',['+c.name+']'
from sys.columns c
JOIN sys.types y ON y.system_type_id = c.system_type_id
where c.[object_id] = OBJECT_ID(@table_name)
and [y].name != 'sysname'
and [y].name != 'timestamp'
order by [c].column_id
FOR XML PATH ('')
)
, 1, 1, '')

insert into @sql(s) values( 'IF EXISTS(SELECT * FROM ['+@table_schema+'].['+@table_name+'])')
insert into @sql(s) values( 'EXEC(''INSERT INTO ['+@table_schema+'].['+@table_name+'_Temp] ('+@cols+')')
insert into @sql(s) values( 'SELECT '+@cols+' FROM ['+@table_schema+'].['+@table_name+']'')')

insert into @sql(s) values( 'SET IDENTITY_INSERT ['+@table_schema+'].['+@table_name+'_Temp] OFF')


insert into @sql(s) values( 'DROP TABLE ['+@table_schema+'].['+@table_name+']')

insert into @sql(s) values( 'EXECUTE sp_rename N''['+@table_schema+'].['+@table_name+'_Temp]'', N'''+@table_name+''', ''OBJECT''')

if ( @pkname is not null ) begin
insert into @sql(s) values('ALTER TABLE ['+@table_schema+'].['+@table_name+'] ADD CONSTRAINT ['+@pkname+'] PRIMARY KEY CLUSTERED (')
insert into @sql(s)
select ' ['+COLUMN_NAME+'] ASC,' from information_schema.key_column_usage
where constraint_name = @pkname
GROUP BY COLUMN_NAME, ordinal_position
order by ordinal_position

-- remove trailing comma
update @sql set s=left(s,len(s)-1) where id=@@identity
insert into @sql(s) values (' )')
end

insert into @sql(s) values ('--Run your Statements')
insert into @sql(s) values ('COMMIT TRANSACTION')
insert into @sql(s) values ('END TRY')
insert into @sql(s) values ('BEGIN CATCH')
insert into @sql(s) values (' ROLLBACK TRANSACTION')
insert into @sql(s) values (' DECLARE @Msg NVARCHAR(MAX) ')
insert into @sql(s) values (' SELECT @Msg=ERROR_MESSAGE() ')
insert into @sql(s) values (' RAISERROR(''Error Occured: %s'', 20, 101,@msg) WITH LOG')
insert into @sql(s) values ('END CATCH')

declare @fqry nvarchar(max)

-- result!
SELECT @fqry = (select char(10) + s from @sql order by id FOR XML PATH (''))


SELECT @table_name as [Table_Name], @fqry as [Generated_Query]
PRINT 'Table: '+@table_name
EXEC sp_executeSql @fqry

FETCH NEXT FROM vendor_cursor
INTO @table_name, @table_schema
END
CLOSE vendor_cursor;
DEALLOCATE vendor_cursor;

**Simple explanation**

Rename the existing column using sp_RENAME

EXEC sp_RENAME 'Table_Name.Existing_ColumnName' , 'New_ColumnName', 'COLUMN'

**Example for Rename :**

The existing column UserID is renamed as OldUserID

EXEC sp_RENAME 'AdminUsers.UserID' , 'OldUserID', 'COLUMN'

Then add a new column using alter query to set as primary key and identity value

ALTER TABLE TableName ADD Old_ColumnName INT NOT NULL PRIMARY KEY IDENTITY(1,1)

**Example for Set Primary key**

The new created column name is UserID

ALTER TABLE Users ADD UserID INT NOT NULL PRIMARY KEY IDENTITY(1,1)

then Drop the Renamed Column

ALTER TABLE Table_Name DROP COLUMN Renamed_ColumnName

**Example for Drop renamed column**

ALTER TABLE Users DROP COLUMN OldUserID

Now we've adding a primarykey and identity to the existing column on the table.