我可以删除一个表，如果它存在使用以下代码，但不知道如何做同样的约束:
IF EXISTS(SELECT 1 FROM sys.objects WHERE OBJECT_ID = OBJECT_ID(N'TableName') AND type = (N'U')) DROP TABLE TableName
go
我还使用以下代码添加了约束:
ALTER TABLE [dbo].[TableName]
WITH CHECK ADD CONSTRAINT [FK_TableName_TableName2] FOREIGN KEY([FK_Name])
REFERENCES [dbo].[TableName2] ([ID])
go
当前回答
ALTER TABLE [dbo].[TableName]
DROP CONSTRAINT FK_TableName_TableName2
其他回答
ALTER TABLE [dbo].[TableName]
DROP CONSTRAINT FK_TableName_TableName2
所有表约束都存储在INFORMATION_SCHEMA中。TABLE_CONSTRAINTS
IF EXISTS(SELECT * FROM INFORMATION_SCHEMA.TABLE_CONSTRAINTS AS C WHERE C.CONSTRAINT_NAME = '<CONSTRAINT NAME>' AND C.TABLE_NAME = '<TABLE NAME>')
BEGIN
ALTER TABLE <TABLE NAME>
DROP CONSTRAINT <CONSTRAINT NAME>
END
GO
对于这个问题，公认的答案似乎对我不起作用。我用稍微不同的方法达到了同样的效果:
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
埃里克·艾萨克斯给出了更简单的答案。但是，它可以在任何表上找到约束。如果你想在一个特定的表上指定一个外键约束，使用这个:
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]
在SQL Server 2016中，你可以使用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
见https://web.archive.org/web/20151105064708/http: / / blogs.msdn.com/b/sqlserverstorageengine/archive/2015/11/03/drop——如果存在-新- sql - server - 2016. - aspx
