設置在表中的唯一值

Question

假設我有一個包含三列的表：UserId TeamId IsTeamCaptain。如何確保每個TeamId的IsTeamCaptain列中只有一個「真實」值？假設我有五個不同的UserId屬於TeamId 1，那麼在這五個中只能有一個是'true'，其餘的必須是'false'。

Answer 1

創建上設置一個獨特的篩選索引（過濾指數是SQL Server 2008中介紹）

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 

這是一個觸發我們的餐桌上