深入了解sql IDENTITY_INSERT,聊聊其对标识列的作用
本篇文章带大家了解下sql IDENTITY_INSERT,介绍一下sql IDENTITY_INSERT对标识列的作用,希望对大家有帮助。
一般情况下,当数据表中,莫一列被设置成了标识列之后,是无法向标识列中手动的去插入标识列的显示值。但是,可以通过设置SET IDENTITY_INSERT属性来实现对标识列中显示值的手动插入。
写法:
1).SET IDENTITY_INSERT 表名 ON :表示开启对标识列显示值插入模式,允许对标识列显示值进行手动插入数据。
2).SET IDENTITY_INSERT 表名 OFF:表示关闭对标识列显示值的插入操作,标识列不允许手动插入显示值。
注意:IDENTITY_INSERT的开启ON和关闭OFF是成对出现的,所以,在执行完手动插入操作之后,记得一定要把IDENTITY_INSERT设置为OFF,否则下次的自动插入数据会插入失败。
例如:
创建一张表b1,b_id为标识列,设置为唯一标识,从1开始,每次插入新数据时,值都递增1,不允许为空:
CREATE table b1
(
b_id int identity(1,1) primary key not null,
b_name varchar(20) null
)
当把表b1中b_id这一列设置为唯一标识列的时候,IDENTITY_INSERT属性的值就默认被设置为了OFF了。标识列b_id列不允许手动去插入显示值,只能由系统自动按照排顺序去插入显示的值。
1.当IDENTITY_INSERT 为OFF时,往表b1中插入2条数据,往标识列中手动插入显示值:
代码1:
insert into b1(b_id,b_name) values(1,'莉莉')
insert into b1(b_id,b_name) values(2,'阿呆')
插入结果:
代码2:
insert into b1(b_name) values('莉莉')
insert into b1(b_name) values('阿呆')
插入结果:
说明:当把IDENTITY_INSERT设置为OFF时,标识列是不允许手动插入显示值的,只能有系统去自动插入标识列的显示值。
2.当IDENTITY_INSERT 为ON时,往表b1中插入2条数据,往标识列中手动插入显示值:
代码1:
set identity_insert b1 on --开启对标识列的插入模式,标识列允许手动插入显示值
insert into b1(b_id,b_name) values(8,'小白') --手动去插入标识列b_id的显示值为8
insert into b1(b_id,b_name) values(9,'小黑')
set identity_insert b1 off --关闭对标识列的插入操作,标识列不允许手动插入显示值
插入结果:
代码2:
set identity_insert b1 on --开启对标识列的插入模式,标识列允许手动插入显示值
insert into b1(b_name) values('小胖') --手动去插入标识列b_id的显示值为8
insert into b1(b_name) values('小宝')
set identity_insert b1 off --关闭对标识列的插入操作,标识列不允许手动插入显示值
插入结果:
说明:当设置IDENTITY_INSERT为ON时,必须要指定标识列中要插入的的显示值,要手动的插入标识列中的显示值。因为系统将不再对标识列的显示值自动插入了。所以,必须要手动去给标识列插入显示值。
推荐学习:mysql视频教程

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