Question

为什么表Room不接受外键？

CREATE TABLE RoomType (
Roomtype nvarchar(2) NOT NULL,
Description nvarchar(20),
Responsibility nvarchar(20),
primary key (Roomtype)
)

Create table Room (
RoomID nvarchar(2) NOT NULL,
Capacity numeric(3)
)
ALTER TABLE Room 
add foreign key(Roomtype)
references RoomType(Roomtype)

这是我运行alter table时收到的错误消息。

重大错误0x80040E11，轻微错误0 更改桌子室添加外键（Roomtype）参考RoomType（Roomtype）列ID无效。 [Roomtype]

Answer 1

在尝试声明外键约束之前，需要将外键作为字段添加到Room表中。

CREATE TABLE RoomType (
Roomtype nvarchar(2) NOT NULL,
Description nvarchar(20),
Responsibility nvarchar(20),
primary key (Roomtype)
)

Create table Room (
RoomID nvarchar(2) NOT NULL,
Capacity numeric(3)
)

ALTER TABLE Room
ADD Roomtype nvarchar(2) NOT NULL

ALTER TABLE Room 
add constraint FK_Give_Me_A_Good_Name foreign key(Roomtype)
references RoomType(Roomtype)

Answer 2

在您可以FK之前，该列必须存在。

CREATE TABLE RoomType (
Roomtype nvarchar(2) NOT NULL,
Description nvarchar(20),
Responsibility nvarchar(20),
primary key (Roomtype)
)

Create table Room (
RoomID nvarchar(2) NOT NULL,
Capacity numeric(3),
RoomtypeA nvarchar(2) NOT NULL
)

ALTER TABLE [dbo].[Room] ADD CONSTRAINT FK_MyName FOREIGN KEY (RoomtypeA) REFERENCES dbo.Roomtype (Roomtype) 
GO

为什么不接受外键？

2 个答案: