设置在表中的唯一值

Question

假设我有一个包含三列的表：UserId TeamId IsTeamCaptain。如何确保每个TeamId的IsTeamCaptain列中只有一个“真实”值？假设我有五个不同的UserId属于TeamId 1，那么在这五个中只能有一个是'true'，其余的必须是'false'。

Answer 1

创建上设置一个独特的筛选索引（过滤指数是SQL Server 2008中介绍）

Answer 2

CREATE TABLE [dbo].[SampleTable](
     [UserID] [int] NOT NULL, 
     [TeamID] [int] NOT NULL, 
     [IsTeamCaptain] [bit] NOT NULL) 
go 

create trigger triu_SampleTable on SampleTable 
instead of insert, update 
as 
begin 
set nocount on 

declare @userid int, @teamid int, @isteamcaptain bit, @counter int 

declare cur cursor local fast_forward for 
select userid, teamid, isteamcaptain from inserted 

open cur 

fetch next from cur into @userid, @teamid, @isteamcaptain 
while @@fetch_status = 0 
begin 
if @isteamcaptain = 0 
    insert into Sampletable(userid, teamid, isteamcaptain) 
    values(@userid, @teamid, @isteamcaptain) 
if @isteamcaptain = 1 
    if exists(select * from SampleTable Where teamid = @teamid and isteamcaptain = 1) 
     raiserror('Not allow to add more than 1 captain per team',16,1) 
    else 
     insert into Sampletable(userid, teamid, isteamcaptain) 
     values(@userid, @teamid, @isteamcaptain) 

fetch next from cur into @userid, @teamid, @isteamcaptain 
end 

close cur 
deallocate cur 

end 
Go 

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