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
好吧，我知道我迟到了，但是下面是我认为最好的语法。如果需要，向OBJECT_ID子句添加模式名。
IF OBJECTPROPERTY(OBJECT_ID(N'My_FK_name'),'IsConstraint') =1
ALTER TABLE dbo.TableName DROP CONSTRAINT My_FK_name
其他回答
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
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
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
IF (OBJECT_ID('DF_Constraint') IS NOT NULL)
BEGIN
ALTER TABLE [dbo].[tableName]
DROP CONSTRAINT DF_Constraint
END
这在Azure Sql服务器上工作得很顺利:
IF (OBJECT_ID('dbo.FK_company_id', 'F') IS NOT NULL)
BEGIN
ALTER TABLE dbo.table_company DROP CONSTRAINT FK_company_id
END
