位列的唯一约束仅允许1个True（1）值 [英] Unique Constraint for Bit Column Allowing Only 1 True (1) Value

问题描述

我有此表：

CREATE TABLE [tblExample](
    [ExampleID] [int] IDENTITY(1,1) NOT NULL,
    [WordsAndStuff] [nvarchar](max) NOT NULL,
    [Active] [bit] NOT NULL

我希望Active列具有唯一的约束，该约束仅允许一条记录为真（1）。这时，我不需要成为一直都是真实记录，最多只能有一个。

I want the Active column to have a unique constraint that will only allow one record to be true (1). At this point, I don't need there to BE a true record all the time, there just cannot be more than one of them.

我该如何写约束？

推荐答案

表中一次只有一个活动记录吗？您可以将唯一索引与过滤器一起使用：

Just one active record at a time in the table? You can use a unique index with a filter:

create unique nonclustered index uixf_tblExample_Active_filtered
  on tblExample (Active)
    include (ExampleId, WordsAndStuff) -- optional included columns
  where Active=1

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