在SQL 2005及以上版本中，有一个技巧可以在不改变表的数据页的情况下解决这个问题。这对于大型表很重要，因为在这些表中，处理每个数据页可能需要花费几分钟或几小时的时间。即使标识列是一个主键，是聚集或非聚集索引的一部分，或者其他可能阻碍更简单的“添加/删除/重命名列”解决方案的陷阱，这个技巧也同样有效。

这里有一个技巧:你可以使用SQL Server的ALTER TABLE…SWITCH语句在不改变数据的情况下更改表的模式，这意味着您可以使用相同的表模式替换IDENTITY表，但没有IDENTITY列。同样的技巧也适用于向现有列添加IDENTITY。

通常，ALTER TABLE…SWITCH用于有效地将分区表中的满分区替换为新的空分区。但它也可以用于非分区表。

我使用这个技巧在不到5秒的时间内将一个25亿行表中的列从IDENTITY转换为非IDENTITY(为了运行一个多小时的查询，其查询计划对非IDENTITY列更有效)，然后在不到5秒的时间内恢复IDENTITY设置。

下面是它如何工作的代码示例。

 CREATE TABLE Test
 (
   id int identity(1,1),
   somecolumn varchar(10)
 );
  
 INSERT INTO Test VALUES ('Hello');
 INSERT INTO Test VALUES ('World');
  
 -- copy the table. use same schema, but no identity
 CREATE TABLE Test2
 (
   id int NOT NULL,
   somecolumn varchar(10)
 );
  
 ALTER TABLE Test SWITCH TO Test2;

 -- drop the original (now empty) table
 DROP TABLE Test;

 -- rename new table to old table's name
 EXEC sp_rename 'Test2','Test';
  
 -- update the identity seed
 DBCC CHECKIDENT('Test');

 -- see same records
 SELECT * FROM Test; 

这显然比其他答案更复杂，但如果您的表很大，这可能是一个真正的救星。这里有一些注意事项:

As far as I know, identity is the only thing you can change about your table's columns with this method. Adding/removing columns, changing nullability, etc. isn't allowed. You'll need to drop foriegn keys before you do the switch and restore them after. Same for WITH SCHEMABINDING functions, views, etc. new table's indexes need to match exactly (same columns, same order, etc.) Old and new tables need to be on the same filegroup. Only works on SQL Server 2005 or later I previously believed that this trick only works on the Enterprise or Developer editions of SQL Server (because partitions are only supported in Enterprise and Developer versions), but Mason G. Zhwiti in his comment below says that it also works in SQL Standard Edition too. I assume this means that the restriction to Enterprise or Developer doesn't apply to ALTER TABLE...SWITCH.

TechNet上有一篇很好的文章详细介绍了上述要求。

更新- Eric Wu在下面评论了关于这个解决方案的重要信息。复制在这里，以确保它得到更多的关注:

这里还有一个值得一提的警告。虽然 新表将愉快地从旧表接收数据，并且所有的 新行将按照标识模式插入 从1开始，如果该列是主键，则可能中断。 考虑立即运行DBCC CHECKIDENT('<newTableName>') 切换。详见msdn.microsoft.com/en-us/library/ms176057.aspx 信息。

If the table is actively being extended with new rows (meaning you don't have much if any downtime between adding IDENTITY and adding new rows, then instead of DBCC CHECKIDENT you'll want to manually set the identity seed value in the new table schema to be larger than the largest existing ID in the table, e.g. IDENTITY (2435457, 1). You might be able to include both the ALTER TABLE...SWITCH and the DBCC CHECKIDENT in a transaction (or not-- haven't tested this) but seems like setting the seed value manually will be easier and safer.

显然，如果没有新行被添加到表中(或者它们只是偶尔添加，比如每天的ETL进程)，那么这种竞争条件就不会发生，因此DBCC CHECKIDENT是可以的。

修改列的标识属性:

In Server Explorer, right-click the table with identity properties you want to modify and click Open Table Definition. The table opens in Table Designer. Clear the Allow nulls check box for the column you want to change. In the Column Properties tab, expand the Identity Specification property. Click the grid cell for the Is Identity child property and choose Yes from the drop-down list. Type a value in the Identity Seed cell. This value will be assigned to the first row in the table. The value 1 will be assigned by default.

就是这样，对我很管用

如果你碰巧使用Visual Studio 2017+

在服务器对象资源管理器中，右键单击表格，选择“视图代码” 向列添加修饰符“IDENTITY” 更新

这将为你做的一切。

为所有没有标识集的主键= bigint的表生成脚本;这将返回每个表的生成脚本列表;

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;

考虑使用SEQUENCE而不是IDENTITY。

在sql server 2014(我不知道低版本)，你可以简单地使用序列。

CREATE SEQUENCE  sequence_name START WITH here_higher_number_than_max_existed_value_in_column INCREMENT BY 1;

ALTER TABLE table_name ADD CONSTRAINT constraint_name DEFAULT NEXT VALUE FOR sequence_name FOR column_name

从这里开始:将序列作为列的默认值

这里有一个很酷的解决方案: 在列上添加或删除标识属性

简而言之，在SQL管理器中手动编辑您的表，切换标识，不要保存更改，只显示将为更改创建的脚本，复制它并稍后使用。

这节省了大量的时间，因为它(脚本)包含了所有与您更改的表相关的外键、索引等。手动写这个…上帝保佑。