sql - sql中两列不能同时为null

Question

假设有一个表叫

员工

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

现在我想设置约束，使得地址和alternateAddress 都不能为空，即可能的情况是：

• 地址为空且alternateAddress 不为空
• alterAddress 为空且地址不为空
• AlternateAddress 不为空且地址不为空

但是不会发生 Employee 表中的任何记录都插入了 alternateAddress 和 address 两者都为空

Answer 1

像这样为您的表创建一个约束：

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

像这样创建你的约束：

(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

根据德摩根定律，not (A and B) 等价于 (not A or not B)，因此

(address is not null OR alternateAddress is not null)

Answer 4

你可以不使用：

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

或者

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

还是那是不好的形式？