参考
if exists (select * from dbo.sysobjects where id = object_id(N'[dbo].[FK_A0630_a0620]') and OBJECTPROPERTY(id, N'IsForeignKey') = 1)
ALTER TABLE [dbo].[A0630] DROP CONSTRAINT FK_A0630_a0620 ---先删除
GO
---再增加
ALTER TABLE [dbo].[A0630] ADD
CONSTRAINT [FK_A0630_a0620] FOREIGN KEY
(
[a]
) REFERENCES [dbo].[a0620] (
[a]
) ON DELETE CASCADE ON UPDATE CASCADE
GO