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：
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/*
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drop table tb
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drop table tb_b
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drop table tb_c
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*/
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--建立3个关联的表
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create table tb(id int primary key ,vv varchar(10))
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-
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create table tb_b(
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idd int primary key,
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id int foreign key references tb(id)
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)
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create table tb_c(
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iddd int primary key,
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idd int foreign key references tb_b(idd)
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)
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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：
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;WITH FK --外键约束
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AS
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(
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SELECT
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SCH.name as foreign_schema_name, --外键schema名
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FK.name as foreign_name, --外键名
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FK.is_disabled , --是否禁用
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FK.delete_referential_action_desc as delete_action,
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FK.update_referential_action_desc as update_action,
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FKC.constraint_column_id, --约束列的id
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FKC.parent_object_id, --父对象的id
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FKC.parent_column_id, --父对象列的id
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FKC.referenced_object_id, --被引用的对象
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FKC.referenced_column_id --被引用的对象中的列
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FROM sys.foreign_keys FK
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INNER JOIN sys.foreign_key_columns FKC
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ON FK.object_id = FKC.constraint_object_id
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INNER JOIN sys.schemas SCH
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ON FK.schema_id = SCH.schema_id
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),
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TB --表和列
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AS
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(
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SELECT
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TB.object_id,
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SCH.name as schema_name,
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TB.name as table_name,
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C.column_id as column_id,
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C.name as column_name
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FROM sys.tables TB WITH(NOLOCK)
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INNER JOIN sys.columns C WITH(NOLOCK)
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ON TB.object_id = C.object_id
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INNER JOIN sys.schemas SCH WITH(NOLOCK)
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ON TB.schema_id = SCH.schema_id
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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
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)
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SELECT
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'alter table ['+TBP.schema_name+'].['+TBP.table_name+
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'] drop constraint ['+FK.foreign_name+'];' as '删除外键的语句,复制出来后运行'
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FROM FK
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INNER JOIN TB TBP
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ON FK.parent_object_id = TBP.object_id
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AND FK.parent_column_id = TBP.column_id
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INNER JOIN TB TBR
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ON FK.referenced_object_id = TBR.object_id
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AND FK.referenced_column_id = TBR.column_id
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/*
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删除外键的语句,复制出来后运行
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alter table [dbo].[tb_b] drop constraint [FK__tb_b__id__6754599E];
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alter table [dbo].[tb_c] drop constraint [FK__tb_c__idd__6C190EBB];
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*/
另外，删除主键后，插入数据，然后再建立外键：
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;WITH FK --外键约束
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AS
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(
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SELECT
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SCH.name as foreign_schema_name, --外键schema名
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FK.name as foreign_name, --外键名
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FK.is_disabled , --是否禁用
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FK.delete_referential_action_desc as delete_action,
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FK.update_referential_action_desc as update_action,
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FKC.constraint_column_id, --约束列的id
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FKC.parent_object_id, --父对象的id
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FKC.parent_column_id, --父对象列的id
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FKC.referenced_object_id, --被引用的对象
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FKC.referenced_column_id --被引用的对象中的列
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FROM sys.foreign_keys FK
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INNER JOIN sys.foreign_key_columns FKC
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ON FK.object_id = FKC.constraint_object_id
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INNER JOIN sys.schemas SCH
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ON FK.schema_id = SCH.schema_id
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),
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TB --表和列
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AS
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(
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SELECT
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TB.object_id,
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SCH.name as schema_name,
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TB.name as table_name,
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C.column_id as column_id,
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C.name as column_name
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FROM sys.tables TB WITH(NOLOCK)
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INNER JOIN sys.columns C WITH(NOLOCK)
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ON TB.object_id = C.object_id
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INNER JOIN sys.schemas SCH WITH(NOLOCK)
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ON TB.schema_id = SCH.schema_id
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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
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)
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SELECT
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'alter table ['+TBP.schema_name+'].['+TBP.table_name+
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'] add constraint ['+FK.foreign_name+'] '+
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' foreign key('+TBP.column_name+') references [' +
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TBR.schema_name +'].['+ TBR.table_name +']('+TBR.column_name+')'
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as '新建外键索引,复制然后在运行'
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FROM FK
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INNER JOIN TB TBP
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ON FK.parent_object_id = TBP.object_id
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AND FK.parent_column_id = TBP.column_id
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INNER JOIN TB TBR
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ON FK.referenced_object_id = TBR.object_id
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AND FK.referenced_column_id = TBR.column_id
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/*
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新建外键索引,复制然后在运行
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alter table [dbo].[tb_c] add constraint [FK__tb_c__idd__0A9D95DB] foreign key(idd) references [dbo].[tb_b](idd)
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alter table [dbo].[tb_b] add constraint [FK__tb_b__id__05D8E0BE] foreign key(id) references [dbo].[tb](id)
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*/
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？
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create table tb(id int primary key ,vv varchar(10))
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insert into tb
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values(1,'aa')
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go
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create table tb_b(
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idd int primary key,
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id int --foreign key references tb(id)
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)
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insert into tb_b
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values(1,2) --id不在主表中
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go
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--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
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ALTER TABLE [dbo].[tb_b] WITH noCHECK ADD FOREIGN KEY([id])
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REFERENCES [dbo].[tb] ([id])
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GO
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--会报错 ，在建立上面的约束后，再次插入，就会报错了
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insert into tb_b
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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
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--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)？
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CREATE TABLE [dbo].[a1](
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[c2] [decimal](10, 2) NULL,
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[c3] [decimal](10, 3) NULL CONSTRAINT [DF_a1_c3] DEFAULT ((0)),
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[re] [bigint] IDENTITY(1,1) NOT NULL,
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CONSTRAINT [PK_a1] PRIMARY KEY CLUSTERED
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(
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[re] ASC
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)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
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) ON [PRIMARY]
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go
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declare @sql varchar(8000),@tablename varchar(100)
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set @tablename ='a1'--这里输入表名
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set @sql = 'create table ['+@tablename+']
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(
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'
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select @sql = @sql + b.name + ' '+
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c.name+
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case when c.collation_name is not null then '('+
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case when b.max_length <>-1 then convert(varchar(100),b.max_length)
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else 'MAX'
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end +') '
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else ''
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end +
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case when b.is_identity = 1 then ' identity('+convert(varchar(100),IDENT_SEED(@tablename))+','+convert(varchar(100),IDENT_INCR(@tablename))+')' else '' end +
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case when d.definition is not null then ' default('+d.definition +')' else '' end +
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case when b.is_nullable = 0 then ' not null' else ' null' end +
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',
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'
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from sys.objects a join sys.columns b
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on a.object_id = b.object_id
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join sys.types c
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on b.system_type_id = c.system_type_id and b.user_type_id = c.user_type_id
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left join sys.default_constraints d
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on b.default_object_id = d.object_id
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where a.name=@tablename
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order by b.column_id
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if exists(select * from sys.indexes where object_id =object_id(@tablename) and is_primary_key =1 )
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begin
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select @sql = @sql + 'CONSTRAINT ['+name+'] PRIMARY KEY '+type_desc+'
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(
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' from sys.indexes where object_id =object_id(@tablename) and is_primary_key =1
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select @sql = @sql + b.name + case when a.is_descending_key =1 then ' DESC' else ' ASC' end +',
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' from sys.index_columns a join sys.columns b
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on a.object_id= b.object_id and a.column_id = b.column_id
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where a.object_id =object_id(@tablename)
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select @sql = left(@sql,len(@sql)-3)+'
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)'
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select @sql = @sql+'
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) ON [PRIMARY] '
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end
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else
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begin
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select @sql = left(@sql,len(@sql)-1)+'
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) ON [PRIMARY] '
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end
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print @sql
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/*
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create table [a1]
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(
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c2 decimal null,
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c3 decimal default(((0))) null,
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re bigint identity(1,1) not null,
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CONSTRAINT [PK_a1] PRIMARY KEY CLUSTERED
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(
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re ASC
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)
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) ON [PRIMARY]
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*/
