【SQL Server DBA】维护语句：删除并创建外键约束、获取建表语句

原文:【SQL Server DBA】维护语句：删除并创建外键约束、获取建表语句

1、删除外键约束，建立外键约束

先建立3个表：

/*





drop table tb





drop table tb_b





drop table tb_c





*/





 





--建立3个关联的表





create table tb(id int primary key ,vv varchar(10))





 





 





create table tb_b(





idd int primary key,





id int foreign key references tb(id)





)





 





create table tb_c(





iddd int primary key,





idd int foreign key references tb_b(idd)





)





go

可以生成删除外键的语句，需要复制出来，然后放到再执行：

;WITH FK  --外键约束





AS





(





	SELECT





		SCH.name as foreign_schema_name,   --外键schema名





		FK.name as foreign_name,           --外键名





		FK.is_disabled ,                   --是否禁用





		





		FK.delete_referential_action_desc as delete_action,





		FK.update_referential_action_desc as update_action,





		





		FKC.constraint_column_id,		   --约束列的id





		FKC.parent_object_id,              --父对象的id





		FKC.parent_column_id,              --父对象列的id





		





		





		FKC.referenced_object_id,          --被引用的对象





		FKC.referenced_column_id           --被引用的对象中的列





	 FROM sys.foreign_keys FK





		INNER JOIN sys.foreign_key_columns FKC





			ON FK.object_id = FKC.constraint_object_id





		INNER JOIN sys.schemas SCH





			ON FK.schema_id = SCH.schema_id





),





 





TB   --表和列





AS





(





	SELECT 





		TB.object_id,





		SCH.name as schema_name,





		TB.name as table_name,





		C.column_id as column_id,





		C.name as column_name		





	FROM sys.tables TB WITH(NOLOCK)





		INNER JOIN sys.columns C WITH(NOLOCK)





			ON TB.object_id = C.object_id





		INNER JOIN sys.schemas SCH WITH(NOLOCK)





			ON TB.schema_id = SCH.schema_id





	WHERE TB.is_ms_shipped = 0  -- 此条件表示仅查询不是由内部 SQL Server 组件创建对象





)





 





SELECT





    'alter table ['+TBP.schema_name+'].['+TBP.table_name+





    '] drop constraint ['+FK.foreign_name+'];' as '删除外键的语句,复制出来后运行'





FROM FK





INNER JOIN TB TBP





		ON FK.parent_object_id = TBP.object_id





		   AND FK.parent_column_id = TBP.column_id





		   





INNER JOIN TB TBR





		ON FK.referenced_object_id = TBR.object_id





		   AND FK.referenced_column_id = TBR.column_id





/*





删除外键的语句,复制出来后运行





alter table [dbo].[tb_b] drop constraint [FK__tb_b__id__6754599E];





alter table [dbo].[tb_c] drop constraint [FK__tb_c__idd__6C190EBB];





*/

另外，删除主键后，插入数据，然后再建立外键：

;WITH FK  --外键约束





AS





(





	SELECT





		SCH.name as foreign_schema_name,   --外键schema名





		FK.name as foreign_name,           --外键名





		FK.is_disabled ,                   --是否禁用





		





		FK.delete_referential_action_desc as delete_action,





		FK.update_referential_action_desc as update_action,





		





		FKC.constraint_column_id,		   --约束列的id





		FKC.parent_object_id,              --父对象的id





		FKC.parent_column_id,              --父对象列的id





		





		





		FKC.referenced_object_id,          --被引用的对象





		FKC.referenced_column_id           --被引用的对象中的列





	 FROM sys.foreign_keys FK





		INNER JOIN sys.foreign_key_columns FKC





			ON FK.object_id = FKC.constraint_object_id





		INNER JOIN sys.schemas SCH





			ON FK.schema_id = SCH.schema_id





),





 





TB   --表和列





AS





(





	SELECT 





		TB.object_id,





		SCH.name as schema_name,





		TB.name as table_name,





		C.column_id as column_id,





		C.name as column_name		





	FROM sys.tables TB WITH(NOLOCK)





		INNER JOIN sys.columns C WITH(NOLOCK)





			ON TB.object_id = C.object_id





		INNER JOIN sys.schemas SCH WITH(NOLOCK)





			ON TB.schema_id = SCH.schema_id





	WHERE TB.is_ms_shipped = 0  -- 此条件表示仅查询不是由内部 SQL Server 组件创建对象





)





 





SELECT





    'alter table ['+TBP.schema_name+'].['+TBP.table_name+





    '] add constraint ['+FK.foreign_name+'] '+





    ' foreign key('+TBP.column_name+') references [' +





    TBR.schema_name +'].['+ TBR.table_name +']('+TBR.column_name+')'





    as '新建外键索引,复制然后在运行'





FROM FK





INNER JOIN TB TBP





		ON FK.parent_object_id = TBP.object_id





		   AND FK.parent_column_id = TBP.column_id





		   





INNER JOIN TB TBR





		ON FK.referenced_object_id = TBR.object_id





		   AND FK.referenced_column_id = TBR.column_id





/*





新建外键索引,复制然后在运行





alter table [dbo].[tb_c] add constraint [FK__tb_c__idd__0A9D95DB]  foreign key(idd) references [dbo].[tb_b](idd)





alter table [dbo].[tb_b] add constraint [FK__tb_b__id__05D8E0BE]  foreign key(id) references [dbo].[tb](id)





*/

另外，还有一个问题：原来两个表之间是有外键的，删除了外键导入数据后，导入的数据记录条数和原表也一致，发现子表有记录不属于主表的，那么原来的外键是怎么建立的？

create table tb(id int primary key ,vv varchar(10))





 





insert into tb





values(1,'aa') 





go





 





create table tb_b(





idd int primary key,





id int --foreign key references tb(id)





)





 





insert into tb_b





values(1,2)  --id不在主表中





go





 





--新增外键约束,不会报错，with nocheck对于之前已经存在的数据，不会进行检测





ALTER TABLE [dbo].[tb_b]  WITH noCHECK ADD FOREIGN KEY([id])





REFERENCES [dbo].[tb] ([id])





GO





 





 





--会报错 ，在建立上面的约束后，再次插入，就会报错了





insert into tb_b





values(2,2)  --id不在主表中

2、如何根据表名查询出创建该表的代码

--当用以下代码创建一个表后，如何根据表名查询出创建该表的代码(也就是以下代码)？





CREATE TABLE [dbo].[a1](





	[c2] [decimal](10, 2) NULL,





	[c3] [decimal](10, 3) NULL CONSTRAINT [DF_a1_c3]  DEFAULT ((0)),





	[re] [bigint] IDENTITY(1,1) NOT NULL,





 CONSTRAINT [PK_a1] PRIMARY KEY CLUSTERED 





(





	[re] ASC





)WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON) ON [PRIMARY]





) ON [PRIMARY]





go

declare @sql varchar(8000),@tablename varchar(100)





set @tablename ='a1'--这里输入表名





set @sql = 'create table ['+@tablename+'] 





(





'





select @sql = @sql + b.name + ' '+





       c.name+





       case when c.collation_name is not null then '('+





         case when b.max_length <>-1 then convert(varchar(100),b.max_length)





           else 'MAX'





         end +') '





        else ''





       end +





       case when b.is_identity = 1 then ' identity('+convert(varchar(100),IDENT_SEED(@tablename))+','+convert(varchar(100),IDENT_INCR(@tablename))+')' else '' end +





       case when d.definition is not null then ' default('+d.definition +')' else '' end +





       case when b.is_nullable = 0 then ' not null' else ' null' end +





       





',





'





from sys.objects a join sys.columns b





on a.object_id = b.object_id





join sys.types c





on b.system_type_id = c.system_type_id and b.user_type_id = c.user_type_id





left join sys.default_constraints d





on b.default_object_id = d.object_id





where a.name=@tablename





order by b.column_id





if exists(select * from sys.indexes where object_id =object_id(@tablename) and is_primary_key =1 )





begin





select @sql = @sql + 'CONSTRAINT ['+name+'] PRIMARY KEY '+type_desc+'





(





' from sys.indexes where object_id =object_id(@tablename) and is_primary_key =1





select @sql = @sql + b.name + case when a.is_descending_key =1 then ' DESC' else ' ASC' end +',





' from sys.index_columns a join sys.columns b





on a.object_id= b.object_id and a.column_id = b.column_id





where a.object_id =object_id(@tablename)





select @sql = left(@sql,len(@sql)-3)+'





)'





select @sql = @sql+'





) ON [PRIMARY] '





end





else





begin





select @sql = left(@sql,len(@sql)-1)+'





) ON [PRIMARY] '





end





print @sql





 





/*





create table [a1] 





(





c2 decimal null,





c3 decimal default(((0))) null,





re bigint identity(1,1) not null,





CONSTRAINT [PK_a1] PRIMARY KEY CLUSTERED





(





re ASC





)





) ON [PRIMARY] 











*/

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