(摘自http://www.sqljunkies.com/WebLog/roman/archive/2005/01/30/7037.aspx， 现在存档在时光倒流机中)

Foreign key constraints and check constraint are very useful for enforcing data integrity and business rules. There are certain scenarios though where it is useful to temporarily turn them off because their behavior is either not needed or could do more harm than good. I sometimes disable constraint checking on tables during data loads from external sources or when I need to script a table drop/recreate with reloading the data back into the table. I usually do it in scenarios where I don't want a time consuming process to fail because one or a few of many million rows have bad data in it. But I always turn the constraints back on once the process is finished and also in some cases I run data integrity checks on the imported data.

如果禁用外键约束，则可以插入父表中不存在的值。如果禁用检查约束，则可以将值放入列中，就像检查约束不存在一样。下面是禁用和启用表约束的一些例子:

——禁用所有表约束 修改表MyTable NOCHECK约束 ——启用所有表约束 修改MyTable，检查检查约束全部 ——禁用单个约束 修改表MyTable NOCHECK约束 ——启用单一约束 ALTER TABLE MyTable WITH CHECK CHECK CONSTRAINT MyConstraint

您可以暂时禁用表上的约束，进行工作，然后重新构建它们。

这里有一个简单的方法…

禁用所有索引，包括主键，这将禁用所有外键，然后重新启用主键，以便您可以使用它们…

DECLARE @sql AS NVARCHAR(max)=''
select @sql = @sql +
    'ALTER INDEX ALL ON [' + t.[name] + '] DISABLE;'+CHAR(13)
from  
    sys.tables t
where type='u'

select @sql = @sql +
    'ALTER INDEX ' + i.[name] + ' ON [' + t.[name] + '] REBUILD;'+CHAR(13)
from  
    sys.key_constraints i
join
    sys.tables t on i.parent_object_id=t.object_id
where
    i.type='PK'


exec dbo.sp_executesql @sql;
go

[做一些事情，比如加载数据]

然后重新启用和重建索引……

DECLARE @sql AS NVARCHAR(max)=''
select @sql = @sql +
    'ALTER INDEX ALL ON [' + t.[name] + '] REBUILD;'+CHAR(13)
from  
    sys.tables t
where type='u'

exec dbo.sp_executesql @sql;
go

最好的选择是DROP和CREATE外键约束。

我在这篇文章中没有找到对我“原样”工作的例子，如果外键引用不同的模式，一个不会工作，如果外键引用多列，另一个也不会工作。这个脚本同时考虑多个模式和每个外键的多个列。

下面是生成“ADD CONSTRAINT”语句的脚本，对于多列，它将用逗号分隔它们(确保在执行DROP语句之前保存此输出):

PRINT N'-- CREATE FOREIGN KEY CONSTRAINTS --';

SET NOCOUNT ON;
SELECT '
PRINT N''Creating '+ const.const_name +'...''
GO
ALTER TABLE ' + const.parent_obj + '
    ADD CONSTRAINT ' + const.const_name + ' FOREIGN KEY (
            ' + const.parent_col_csv + '
            ) REFERENCES ' + const.ref_obj + '(' + const.ref_col_csv + ')
GO'
FROM (
    SELECT QUOTENAME(fk.NAME) AS [const_name]
        ,QUOTENAME(schParent.NAME) + '.' + QUOTENAME(OBJECT_name(fkc.parent_object_id)) AS [parent_obj]
        ,STUFF((
                SELECT ',' + QUOTENAME(COL_NAME(fcP.parent_object_id, fcp.parent_column_id))
                FROM sys.foreign_key_columns AS fcP
                WHERE fcp.constraint_object_id = fk.object_id
                FOR XML path('')
                ), 1, 1, '') AS [parent_col_csv]
        ,QUOTENAME(schRef.NAME) + '.' + QUOTENAME(OBJECT_NAME(fkc.referenced_object_id)) AS [ref_obj]
        ,STUFF((
                SELECT ',' + QUOTENAME(COL_NAME(fcR.referenced_object_id, fcR.referenced_column_id))
                FROM sys.foreign_key_columns AS fcR
                WHERE fcR.constraint_object_id = fk.object_id
                FOR XML path('')
                ), 1, 1, '') AS [ref_col_csv]
    FROM sys.foreign_key_columns AS fkc
    INNER JOIN sys.foreign_keys AS fk ON fk.object_id = fkc.constraint_object_id
    INNER JOIN sys.objects AS oParent ON oParent.object_id = fkc.parent_object_id
    INNER JOIN sys.schemas AS schParent ON schParent.schema_id = oParent.schema_id
    INNER JOIN sys.objects AS oRef ON oRef.object_id = fkc.referenced_object_id
    INNER JOIN sys.schemas AS schRef ON schRef.schema_id = oRef.schema_id
    GROUP BY fkc.parent_object_id
        ,fkc.referenced_object_id
        ,fk.NAME
        ,fk.object_id
        ,schParent.NAME
        ,schRef.NAME
    ) AS const
ORDER BY const.const_name

下面是生成“DROP CONSTRAINT”语句的脚本:

PRINT N'-- DROP FOREIGN KEY CONSTRAINTS --';

SET NOCOUNT ON;

SELECT '
PRINT N''Dropping ' + fk.NAME + '...''
GO
ALTER TABLE [' + sch.NAME + '].[' + OBJECT_NAME(fk.parent_object_id) + ']' + ' DROP  CONSTRAINT ' + '[' + fk.NAME + ']
GO'
FROM sys.foreign_keys AS fk
INNER JOIN sys.schemas AS sch ON sch.schema_id = fk.schema_id
ORDER BY fk.NAME

(摘自http://www.sqljunkies.com/WebLog/roman/archive/2005/01/30/7037.aspx， 现在存档在时光倒流机中)

Foreign key constraints and check constraint are very useful for enforcing data integrity and business rules. There are certain scenarios though where it is useful to temporarily turn them off because their behavior is either not needed or could do more harm than good. I sometimes disable constraint checking on tables during data loads from external sources or when I need to script a table drop/recreate with reloading the data back into the table. I usually do it in scenarios where I don't want a time consuming process to fail because one or a few of many million rows have bad data in it. But I always turn the constraints back on once the process is finished and also in some cases I run data integrity checks on the imported data.

如果禁用外键约束，则可以插入父表中不存在的值。如果禁用检查约束，则可以将值放入列中，就像检查约束不存在一样。下面是禁用和启用表约束的一些例子:

——禁用所有表约束 修改表MyTable NOCHECK约束 ——启用所有表约束 修改MyTable，检查检查约束全部 ——禁用单个约束 修改表MyTable NOCHECK约束 ——启用单一约束 ALTER TABLE MyTable WITH CHECK CHECK CONSTRAINT MyConstraint

一个脚本来管理它们:这个脚本将截断和删除命令与sp_MSforeachtable结合在一起，这样您就可以避免删除和重新创建约束——只需指定需要删除而不是截断的表，为了便于度量，我还包含了一个额外的模式过滤器(在2008r2中测试)。

declare @schema nvarchar(max) = 'and Schema_Id=Schema_id(''Value'')'
declare @deletiontables nvarchar(max) = '(''TableA'',''TableB'')'
declare @truncateclause nvarchar(max) = @schema + ' and o.Name not in ' +  + @deletiontables;
declare @deleteclause nvarchar(max) = @schema + ' and o.Name in ' + @deletiontables;        

exec sp_MSforeachtable 'alter table ? nocheck constraint all', @whereand=@schema
exec sp_MSforeachtable 'truncate table ?', @whereand=@truncateclause
exec sp_MSforeachtable 'delete from ?', @whereand=@deleteclause
exec sp_MSforeachtable 'alter table ? with check check constraint all', @whereand=@schema

右键单击表设计，进入“关系”，在左侧窗格中选择外键，在右侧窗格中，将强制外键约束设置为“Yes”(启用外键约束)或“No”(禁用外键约束)。