如何在SQL Server中仅在外键约束存在时删除它？

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如何在SQL Server中仅在外键约束存在时删除它？

我可以使用以下代码删除已存在的表，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

我也可以使用以下代码添加约束：

ALTER TABLE [dbo].[TableName] 
  WITH CHECK ADD CONSTRAINT [FK_TableName_TableName2] FOREIGN KEY([FK_Name])
    REFERENCES [dbo].[TableName2] ([ID])
go

admin 更改状态以发布 2023年5月23日
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2 答案

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在 Eric Isaacs 的答案中提供了更简单的解决方案。然而，它将会在任何表格中查找约束。如果你想要定位特定表格上的外键约束，请使用以下内容：

IF EXISTS (SELECT * 
  FROM sys.foreign_keys 
   WHERE object_id = OBJECT_ID(N'FK_TableName_TableName2')
   AND parent_object_id = OBJECT_ID(N'dbo.TableName')
)
  ALTER TABLE [dbo].[TableName] DROP CONSTRAINT [FK_TableName_TableName2]

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这比当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

如果你需要放弃另一种类型的约束,这些是可以传递到 OBJECT_ID() 函数的第二个参数位置的适用代码:

C = CHECK constraint
D = DEFAULT (constraint or stand-alone)
F = FOREIGN KEY constraint
PK = PRIMARY KEY constraint
UQ = UNIQUE constraint

您也可以使用没有第二个参数的 OBJECT_ID。

类型的完整列表在此处:

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

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