在我们的业务中，我们经常碰到去掉表的identity属性的需求。但是sql并没有提供可以直接去掉该属性的sql语句。但是其实我们自己可以通过三种方式来实现。
第一种：通过界面操作
将以上图中的yes改为no ，然后点击保存，这里需要注意一个问题，sql server好像默认是不允许这样改，这里我们就需要修改一个选项
需要将以上红色框内的选项去掉，这样就可以保存修改，并且保存修改所使用的脚本。
第二种方式，其实就跟上面类似，只是我们可以按照它的原理通过脚本实现。
1 use Test 2 go 3 if OBJECT_ID(‘dbo.RemoveIdentiyTest‘) is not null 4 drop table dbo.RemoveIdentiyTest 5 go 6 --新建一个测试表 7 create table dbo.RemoveIdentiyTest 8 ( 9 id int identity not null, 10 col1 varchar(10) not null constraint DF_RemoveIdentiyTest_col1 default ‘aaa‘, 11 col2 varchar(10) null, 12 col3 int null, 13 col4 int null, 14 col5 char(10) null 15 constraint PK_RemoveIdentiyTest primary key clustered 16 ( 17 id asc 18 ) 19 ) ON [PRIMARY] 20 go 21 create nonclustered index IX_RemoveIdentiyTest_col3_col4 on dbo.RemoveIdentiyTest 22 ( 23 col3,col4 24 )with(fillfactor=80) on [primary] 25 go 26 create nonclustered index IX_RemoveIdentiyTest_col5 on dbo.RemoveIdentiyTest 27 ( 28 col5 29 )with(fillfactor=80)on [primary] 30 31 --method 2：insert date into a tempoprary table 32 BEGIN TRANSACTION 33 GO 34 --为了保证临时表中的数据与原表保持一致，我们要在插入数据前给临时表加对应的默认值约束，但是同一个数据库不能建名称一样的约束，
--所以这里我们先删除原表的约束，这个操作并不影响现存表中的数据 35 ALTER TABLE dbo.RemoveIdentiyTest 36 DROP CONSTRAINT DF_RemoveIdentiyTest_col1 37 GO 38 --新建一个临时表 39 CREATE TABLE dbo.Tmp_RemoveIdentiyTest 40 ( 41 id int NOT NULL, 42 col1 varchar(10) NOT NULL, 43 col2 varchar(10) NULL, 44 col3 int NULL, 45 col4 int NULL, 46 col5 char(10) NULL 47 ) ON [PRIMARY] 48 GO 49 --给临时表加锁 50 ALTER TABLE dbo.Tmp_RemoveIdentiyTest SET (LOCK_ESCALATION = TABLE) 51 GO 52 --为了保证临时表中的数据与原表保持一致，我们要在插入数据前给临时表加对应的默认值约束 53 ALTER TABLE dbo.Tmp_RemoveIdentiyTest ADD CONSTRAINT 54 DF_RemoveIdentiyTest_col1 DEFAULT (‘aaa‘) FOR col1 55 GO 56 --导数据 57 IF EXISTS(SELECT * FROM dbo.RemoveIdentiyTest) 58 EXEC(‘INSERT INTO dbo.Tmp_RemoveIdentiyTest (id, col1, col2, col3, col4, col5) 59 SELECT id, col1, col2, col3, col4, col5 FROM dbo.RemoveIdentiyTest WITH (HOLDLOCK TABLOCKX)‘) 60 GO 61 --删除原表 62 DROP TABLE dbo.RemoveIdentiyTest 63 GO 64 --将临时表更名为正式表 65 EXECUTE sp_rename N‘dbo.Tmp_RemoveIdentiyTest‘, N‘RemoveIdentiyTest‘, ‘OBJECT‘ 66 GO 67 --添加相应的索引 68 ALTER TABLE dbo.RemoveIdentiyTest ADD CONSTRAINT 69 PK_RemoveIdentiyTest PRIMARY KEY CLUSTERED 70 ( 71 id 72 ) WITH( STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY] 73 74 GO 75 CREATE NONCLUSTERED INDEX IX_RemoveIdentiyTest_col3_col4 ON dbo.RemoveIdentiyTest 76 ( 77 col3, 78 col4 79 ) WITH( PAD_INDEX = OFF, FILLFACTOR = 80, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY] 80 GO 81 CREATE NONCLUSTERED INDEX IX_RemoveIdentiyTest_col5 ON dbo.RemoveIdentiyTest 82 ( 83 col5 84 ) WITH( PAD_INDEX = OFF, FILLFACTOR = 80, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY] 85 GO 86 COMMIT
方法三：也是通过脚本实现，但是这里我们使用switch to的方式导数据（这是从分区表借鉴过来的），当然这个两个表switch to有一些限制条件，比如两个表有相同的表结构，两个表必须在同一个数据库等。
1 use Test 2 go 3 if OBJECT_ID(‘dbo.RemoveIdentiyTest‘) is not null 4 drop table dbo.RemoveIdentiyTest 5 go 6 --新建一个测试表 7 create table dbo.RemoveIdentiyTest 8 ( 9 id int identity not null, 10 col1 varchar(10) not null constraint DF_RemoveIdentiyTest_col1 default ‘aaa‘, 11 col2 varchar(10) null, 12 col3 int null, 13 col4 int null, 14 col5 char(10) null 15 constraint PK_RemoveIdentiyTest primary key clustered 16 ( 17 id asc 18 ) 19 ) ON [PRIMARY] 20 go 21 create nonclustered index IX_RemoveIdentiyTest_col3_col4 on dbo.RemoveIdentiyTest 22 ( 23 col3,col4 24 )with(fillfactor=80) on [primary] 25 go 26 create nonclustered index IX_RemoveIdentiyTest_col5 on dbo.RemoveIdentiyTest 27 ( 28 col5 29 )with(fillfactor=80)on [primary] 30 31 go 32 33 --插入测试数据 34 declare @i int,@a int,@b int 35 set @i=0 36 set @a=10000 37 set @b=0 38 while(@i<100000) 39 begin 40 insert into dbo.RemoveIdentiyTest 41 select ‘aa‘+cast(@i as varchar)+‘ff‘,‘bb‘+cast(@i as varchar)+‘dd‘,@a,@b,‘A‘+cast(@i as varchar) 42 set @i=@i+1; 43 set @a=@a-1; 44 set @b=@b+2; 45 end 46 go 47 48 begin try 49 begin transaction 50 51 alter table dbo.RemoveIdentiyTest drop constraint DF_RemoveIdentiyTest_col1 52 if OBJECT_ID(‘dbo.tmp_RemoveIdentiyTest‘) is not null 53 drop table dbo.tmp_RemoveIdentiyTest 54 create table dbo.tmp_RemoveIdentiyTest 55 ( 56 id int not null, 57 col1 varchar(10) not null, 58 col2 varchar(10) null, 59 col3 int null, 60 col4 int null, 61 col5 char(10) null 62 constraint PK_tmp_RemoveIdentiyTest primary key clustered 63 ( 64 id asc 65 ) 66 ) ON [PRIMARY] 67 68 create nonclustered index IX_tmp_RemoveIdentiyTest_col3_col4 on dbo.tmp_RemoveIdentiyTest 69 ( 70 col3,col4 71 )with(fillfactor=80) on [primary] 72 73 create nonclustered index IX_tmp_RemoveIdentiyTest_col5 on dbo.tmp_RemoveIdentiyTest 74 ( 75 col5 76 )with(fillfactor=80)on [primary] 77 --这里使用switch to的方式，比insert 导数据的效率要高很多 78 alter table dbo.RemoveIdentiyTest SWITCH to dbo.tmp_RemoveIdentiyTest 79 alter table dbo.tmp_RemoveIdentiyTest add constraint DF_RemoveIdentiyTest_col1 DEFAULT (‘aaa‘) FOR col1 80 drop table dbo.RemoveIdentiyTest 81 exec sp_rename N‘Test.dbo.tmp_RemoveIdentiyTest.IX_tmp_RemoveIdentiyTest_col3_col4‘,N‘IX_RemoveIdentiyTest_col3_col4‘,N‘index‘ 82 exec sp_rename N‘Test.dbo.tmp_RemoveIdentiyTest.IX_tmp_RemoveIdentiyTest_col5‘,N‘IX_RemoveIdentiyTest_col5‘,N‘INDEX‘ 83 exec sp_rename N‘PK_tmp_RemoveIdentiyTest‘,N‘PK_RemoveIdentiyTest‘,N‘object‘ 84 exec sp_rename ‘Tmp_RemoveIdentiyTest‘, ‘RemoveIdentiyTest‘,‘object‘ 85 commit 86 end try 87 begin catch 88 print ‘error‘ 89 rollback tran 90 end catch
对于以上三种方式，我个人认为如果数据量不是很大，我们可以直接采用第一种或者第二种，但是如果数据量比较大，我们没有足够的磁盘空间或者修改该表所需时间紧迫的情况下，我们可以采用第三种方式。
原文地址：http://www.cnblogs.com/shihuai355/p/3818472.html
