我可以使用以下代码删除表，但不知道如何使用约束执行相同操作：
IF EXISTS(SELECT 1 FROM sys.objects WHERE OBJECT_ID = OBJECT_ID(N'TableName') AND type = (N'U')) DROP TABLE TableName
go
我还使用此代码添加约束：
ALTER TABLE [dbo].[TableName]
WITH CHECK ADD CONSTRAINT [FK_TableName_TableName2] FOREIGN KEY([FK_Name])
REFERENCES [dbo].[TableName2] ([ID])
go
答案 0 :(得分：294)
Eric Isaacs的回答提供了更简单的解决方案。但是，它会在任何表上找到约束。如果要在特定表上定位外键约束，请使用：
IF EXISTS (SELECT *
FROM sys.foreign_keys
WHERE object_id = OBJECT_ID(N'dbo.FK_TableName_TableName2')
AND parent_object_id = OBJECT_ID(N'dbo.TableName')
)
ALTER TABLE [dbo.TableName] DROP CONSTRAINT [FK_TableName_TableName2]
答案 1 :(得分：278)
这比目前提出的解决方案简单得多：
IF (OBJECT_ID('dbo.FK_ConstraintName', 'F') IS NOT NULL)
BEGIN
ALTER TABLE dbo.TableName DROP CONSTRAINT FK_ConstraintName
END
如果您需要删除另一种类型的约束，这些是在第二个参数位置传递到OBJECT_ID（）函数的适用代码：
C = CHECK constraint
D = DEFAULT (constraint or stand-alone)
F = FOREIGN KEY constraint
PK = PRIMARY KEY constraint
UQ = UNIQUE constraint
您也可以在没有第二个参数的情况下使用OBJECT_ID。
完整的类型列表here：
对象类型：
AF = Aggregate function (CLR) C = CHECK constraint D = DEFAULT (constraint or stand-alone) F = FOREIGN KEY constraint FN = SQL scalar function FS = Assembly (CLR) scalar-function FT = Assembly (CLR) table-valued function IF = SQL inline table-valued function IT = Internal table P = SQL Stored Procedure PC = Assembly (CLR) stored-procedure PG = Plan guide PK = PRIMARY KEY constraint R = Rule (old-style, stand-alone) RF = Replication-filter-procedure S = System base table SN = Synonym SO = Sequence object
适用于：SQL Server 2012到SQL Server 2014。
SQ = Service queue TA = Assembly (CLR) DML trigger TF = SQL table-valued-function TR = SQL DML trigger TT = Table type U = Table (user-defined) UQ = UNIQUE constraint V = View X = Extended stored procedure
答案 2 :(得分：22)
在SQL Server 2016中，您可以使用DROP IF EXISTS：
CREATE TABLE t(id int primary key,
parentid int
constraint tpartnt foreign key references t(id))
GO
ALTER TABLE t
DROP CONSTRAINT IF EXISTS tpartnt
GO
DROP TABLE IF EXISTS t
答案 3 :(得分：15)
IF (OBJECT_ID('DF_Constraint') IS NOT NULL)
BEGIN
ALTER TABLE [dbo].[tableName]
DROP CONSTRAINT DF_Constraint
END
答案 4 :(得分：14)
如果您知道实际约束的名称，James的答案就可以了。棘手的是，在遗留场景和其他真实场景中，您可能知道所谓的约束。
如果是这种情况，您可能会冒险创建重复约束，以避免您可以使用：
create function fnGetForeignKeyName
(
@ParentTableName nvarchar(255),
@ParentColumnName nvarchar(255),
@ReferencedTableName nvarchar(255),
@ReferencedColumnName nvarchar(255)
)
returns nvarchar(255)
as
begin
declare @name nvarchar(255)
select @name = fk.name from sys.foreign_key_columns fc
join sys.columns pc on pc.column_id = parent_column_id and parent_object_id = pc.object_id
join sys.columns rc on rc.column_id = referenced_column_id and referenced_object_id = rc.object_id
join sys.objects po on po.object_id = pc.object_id
join sys.objects ro on ro.object_id = rc.object_id
join sys.foreign_keys fk on fk.object_id = fc.constraint_object_id
where
po.object_id = object_id(@ParentTableName) and
ro.object_id = object_id(@ReferencedTableName) and
pc.name = @ParentColumnName and
rc.name = @ReferencedColumnName
return @name
end
go
declare @name nvarchar(255)
declare @sql nvarchar(4000)
-- hunt for the constraint name on 'Badges.BadgeReasonTypeId' table refs the 'BadgeReasonTypes.Id'
select @name = dbo.fnGetForeignKeyName('dbo.Badges', 'BadgeReasonTypeId', 'dbo.BadgeReasonTypes', 'Id')
-- if we find it, the name will not be null
if @name is not null
begin
set @sql = 'alter table Badges drop constraint ' + replace(@name,']', ']]')
exec (@sql)
end
答案 5 :(得分：6)
ALTER TABLE [dbo].[TableName]
DROP CONSTRAINT FK_TableName_TableName2
答案 6 :(得分：3)
Declare @FKeyRemoveQuery NVarchar(max)
IF EXISTS(SELECT 1 FROM sys.foreign_keys WHERE parent_object_id = OBJECT_ID(N'dbo.TableName'))
BEGIN
SELECT @FKeyRemoveQuery='ALTER TABLE dbo.TableName DROP CONSTRAINT [' + LTRIM(RTRIM([name])) + ']'
FROM sys.foreign_keys
WHERE parent_object_id = OBJECT_ID(N'dbo.TableName')
EXECUTE Sp_executesql @FKeyRemoveQuery
END
答案 7 :(得分：1)
我认为这会对你有所帮助......
DECLARE @ConstraintName nvarchar(200)
SELECT
@ConstraintName = KCU.CONSTRAINT_NAME
FROM INFORMATION_SCHEMA.REFERENTIAL_CONSTRAINTS AS RC
INNER JOIN INFORMATION_SCHEMA.KEY_COLUMN_USAGE AS KCU
ON KCU.CONSTRAINT_CATALOG = RC.CONSTRAINT_CATALOG
AND KCU.CONSTRAINT_SCHEMA = RC.CONSTRAINT_SCHEMA
AND KCU.CONSTRAINT_NAME = RC.CONSTRAINT_NAME
WHERE
KCU.TABLE_NAME = 'TABLE_NAME' AND
KCU.COLUMN_NAME = 'TABLE_COLUMN_NAME'
IF @ConstraintName IS NOT NULL EXEC('alter table TABLE_NAME drop CONSTRAINT ' + @ConstraintName)
它将根据特定的表和列删除外键约束。
答案 8 :(得分：0)
您可以使用这些查询查找表格的所有FK。
Declare @SchemaName VarChar(200) = 'Schema Name'
Declare @TableName VarChar(200) = 'Table name'
-- Find FK in This table.
SELECT
'IF EXISTS (SELECT * FROM sys.foreign_keys WHERE object_id = OBJECT_ID(N''' +
'[' + OBJECT_SCHEMA_NAME(FK.parent_object_id) + '].[' + FK.name + ']'
+ ''') AND parent_object_id = OBJECT_ID(N''' +
'[' + OBJECT_SCHEMA_NAME(FK.parent_object_id) + '].['
+ OBJECT_NAME(FK.parent_object_id) + ']' + ''')) ' +
'ALTER TABLE ' + OBJECT_SCHEMA_NAME(FK.parent_object_id) +
'.[' + OBJECT_NAME(FK.parent_object_id) +
'] DROP CONSTRAINT ' + FK.name
, S.name , O.name, OBJECT_NAME(FK.parent_object_id)
FROM sys.foreign_keys AS FK
INNER JOIN Sys.objects As O
ON (O.object_id = FK.parent_object_id )
INNER JOIN SYS.schemas AS S
ON (O.schema_id = S.schema_id)
WHERE
O.name = @TableName
And S.name = @SchemaName
-- Find the FKs in the tables in which this table is used
SELECT
' IF EXISTS (SELECT * FROM sys.foreign_keys WHERE object_id = OBJECT_ID(N''' +
'[' + OBJECT_SCHEMA_NAME(FK.parent_object_id) + '].[' + FK.name + ']'
+ ''') AND parent_object_id = OBJECT_ID(N''' +
'[' + OBJECT_SCHEMA_NAME(FK.parent_object_id) + '].['
+ OBJECT_NAME(FK.parent_object_id) + ']' + ''')) ' +
' ALTER TABLE ' + OBJECT_SCHEMA_NAME(FK.parent_object_id) +
'.[' + OBJECT_NAME(FK.parent_object_id) +
'] DROP CONSTRAINT ' + FK.name
, S.name , O.name, OBJECT_NAME(FK.parent_object_id)
FROM sys.foreign_keys AS FK
INNER JOIN Sys.objects As O
ON (O.object_id = FK.referenced_object_id )
INNER JOIN SYS.schemas AS S
ON (O.schema_id = S.schema_id)
WHERE
O.name = @TableName
And S.name = @SchemaName
答案 9 :(得分：0)
这个问题的接受答案对我来说似乎不起作用。我用稍微不同的方法实现了同样的目的：
IF (select object_id from sys.foreign_keys where [name] = 'FK_TableName_TableName2') IS NOT NULL
BEGIN
ALTER TABLE dbo.TableName DROP CONSTRAINT FK_TableName_TableName2
END
答案 10 :(得分：0)
好的，我知道我迟到了，但是这是我认为最好的语法。如果需要，可以将模式名称添加到OBJECT_ID子句中。
IF OBJECTPROPERTY(OBJECT_ID(N'My_FK_name'),'IsConstraint') =1
ALTER TABLE dbo.TableName DROP CONSTRAINT My_FK_name