Question

假设有一个名为

的表

员工

ID number, name varchar(24 char), address varchar2(100 char), alternateAddress(100 char), sex varchar2(10 char)

现在我想放置约束，使地址和alternateAddress都不能为空，即可能的情况是：

address为null且alternateAddress不为null
alternateAddress为空且地址不为空
alternateAddress不为null且地址不为空

但不能发生Employee表中的任何记录与alternateAddress一起插入并且地址都为null

Answer 1

为您的表创建一个约束，如下所示：

ALTER TABLE [dbo].[Employee]  WITH CHECK ADD  CONSTRAINT [CK_OneAddress] CHECK  ((NOT [address] IS NULL) OR (NOT [alternateAddress] IS NULL))
GO

ALTER TABLE [dbo].[Employee] CHECK CONSTRAINT [CK_OneAddress]
GO

Answer 2

像这样创建约束：

(address is null and alternateAddress is not null) or 
(alternateAddress is null and address is not null) or 
(alternateAddress is not null and address is not null)

Answer 3

因此，根据德摩根定律，（A和B）不等于（不是A或不是B）

(address is not null OR alternateAddress is not null)

Answer 4

您不能使用：

IF(COALESCE(address, alternateAddress) IS NOT NULL)

或

WHERE (COALESCE(address, alternateAddress) IS NOT NULL)

那是不好的形式吗？

在sql中，两列不能同时为null

4 个答案: