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laravel 插入数据的时候，任我怎么插入，也还是这个错误， 不懂为什么我的主键的id ，之前的数据有一条值为‘0’。 

这条错误是


  
违反完整性约束;


把id为0 的改了，就可以了

昨天为了删除数据库表中的字段，使用了
alter table
drop column
columnName
服务器返回的错误为：
Server: Msg 5074, Level 16, State 1, Line 1The object 'DF__Test__columnName__351DDF8C' is dependent on column 'columnName'.
Server: Msg 4922, Level 16, State 1, Line 1
ALTER TABLE DROP COLUMN columnName failed because one or more objects access this column.
我进入企业管理器中却可以删除，
经过检查发现该字段设置有默认值，其实设置了默认值就相当于设置了约束，在Sql Server 2000中约束有以下几种：
1 primary key 主键约束
2 foreign key 外键约束
3 unique 唯一约束
4 check 检查约束
5 default 默认值约束
其中 primary key 主键约束 和 unique 唯一约束 相似但是还是有细微区别：
unique在下面两个情况下可以使用：
1 unique约束可以多个列组合，一个表只可以有一个primary key 约束，而可以有多个unique约束。
2 primary key 约束不能有null，而unique约束可以有null值。
foreign key 和 check约束有相似也有区别
foreign key 约束通过从另外一个表获得有效数值列表，而check约束是从设置在表中的逻辑表达式来判断的。
那现在的问题是：我可以在企业管理器中删除有约束的列而在程序中用：
alter table
drop column
columnName却会出错，那么必须在删除列的时候先删除该列相关的约束了，还好现在是internet时代，上网搜索了一下发现有如下解决方法：
if exists (select * from dbo.sysobjects where id = object_id(N'[dbo].[p_deletefield]') and OBJECTPROPERTY(id, N'IsProcedure') = 1)
drop procedure [dbo].[p_deletefield]
GO
/*--删除某字段的所有关系及该字段
删除某字段时,常常因为在该字段上定义了约束/外键/默认值
导致字段删除失败,此存储过就是删除表中指定字段的这些关系
修正2004.05发布的删除处理中的错误,同时改原来的处理语句为通用存储过程
--邹建 2004.07--*/
/*--调用示例
exec p_deletefield '表名','字段名'
--*/
create proc p_deletefield
@tbname sysname, --要处理的表名
@fdname sysname, --要处理的字段名
@delfield bit=1  --0只删除关系,1同时删除字段
as
declare hCForEach cursor global for
--默认值约束
select sql='alter table ['+b.name+'] drop constraint ['+d.name+']'
from syscolumns a
join sysobjects b on a.id=b.id and a.name=@fdname and b.name=@tbname
join syscomments c on a.cdefault=c.id
join sysobjects d on c.id=d.id
union --外键引用
select s='alter table ['+c.name+'] drop constraint ['+b.name+']'
from sysforeignkeys a
join sysobjects b on b.id=a.constid
join sysobjects c on c.id=a.fkeyid
join syscolumns d on d.id=c.id and a.fkey=d.colid and d.name=@fdname
join sysobjects e on e.id=a.rkeyid and e.name=@tbname
join syscolumns f on f.id=e.id and a.rkey=f.colid
union --主键/唯一键/索引
select case when e.xtype in('PK','UQ') then 'alter table ['+c.name+'] drop constraint ['+e.name+']'
else 'drop index ['+c.name+'].['+a.name+']' end
from sysindexes a
join sysindexkeys b on a.id=b.id and a.indid=b.indid
join sysobjects c on b.id=c.id and c.xtype='U' and c.name=@tbname
join syscolumns d on b.id=d.id and b.colid=d.colid and d.name=@fdname
left join sysobjects e on e.id=object_id(a.name)
where a.indid not in(0,255)
exec sp_msforeach_worker '?'
if @delfield=1
exec('alter table ['+@tbname+'] drop column ['+@fdname+']')
go

Encounter local execpiton: android.database.sqlite.SQLiteConstraintException: UNIQUE constraint failed: greendao-db._id (code 1555)

违反唯一性约束 你对表做create和update的时候对该字段的插入值重复了