SQL Server 2008检查约束不起作用

Question

CREATE TABLE [dbo].[StateMaster]([StateId] [int] IDENTITY(1,1) NOT NULL,[StateName] [varchar](30) NOT NULL,[IsDisable] [bit] NOT NULL,CONSTRAINT CHK_StateDisable CHECK *(**IsDisable>=0 and IsDisable<=1**)*,
CONSTRAINT [PK_StateMaster] PRIMARY KEY CLUSTERED 
(
    [StateId] ASC
)WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON) ON [PRIMARY]
) ON [PRIMARY]

GO

SET ANSI_PADDING OFF
GO

ALTER TABLE [dbo].[StateMaster] ADD  CONSTRAINT [DF_StateMaster_IsDisable]  DEFAULT ((0)) FOR [IsDisable]
GO

执行此插入后：

insert into StateMaster values ('ABC',***2***)`

我得到这个输出：

select * from StateMaster


StateId StateName   IsDisable
1       ABC         **1**

Answer 1

您没有得到预期的输出，因为您将列IsDisable定义为BIT，它只能接受True / False或1/0。所以对于BIT数据类型，除0和NULL之外的所有值都是1。

SELECT CAST(NULL AS BIT),
       CAST(0 AS BIT),
       CAST(1 AS BIT),
       CAST(4 AS BIT);

给你以下结果

因此，您可以尝试将IsDisable的数据类型更改为INT，然后尝试相同的插入。 Iwillll抛出以下错误

消息547，级别16，状态0，行17 INSERT语句与CHECK约束“CHK_StateDisable”冲突。冲突发生在数据库“MyDb”，表“dbo.StateMaster”，列“IsDisable”中。该语句已终止。