在SQL Server

Question

我需要拿一张桌子，其中包含偶数队伍的名称，并为那些比赛生成赛程表，即如果有4个队伍：team1，team2，team3和team4在表格中，那么结果表将如下所示

Team    Team     Round
-----------------------
team1   team2    1
team 3  team4    1
team1   team3    2
team2   team4    2
team1   team4    3
team2   team3    3

我需要使用T-SQL执行此操作。我尝试过使用Round Robin Tournament算法，但我不知道如何在T-SQL中实现它。

Answer 1

看到没有其他人给出了这个答案，我想我可能会向您展示一种（可能效率低下）使用动态SQL执行此操作的方法：

DECLARE @SQL NVARCHAR(MAX) = N'';
SELECT TOP (SELECT CASE COUNT(*) % 2 WHEN 1 THEN COUNT(*) ELSE COUNT(*) - 1 END FROM dbo.Teams) @SQL += N' UNION ALL
SELECT *
FROM
(
    SELECT TOP (SELECT COUNT(*) / 2 FROM T) 
        Team, 
        RN, 
        RoundNum = ' + CAST(N AS NVARCHAR(3)) + N', 
        Match = ROW_NUMBER() OVER (ORDER BY CASE WHEN RN = 1 THEN 0 ELSE 1 END, (RN + ' + CAST(N - 2 AS NVARCHAR(3)) + N') % (SELECT COUNT(*) FROM T)),
        Slot = 1
    FROM T
    ORDER BY CASE WHEN RN = 1 THEN 0 ELSE 1 END, (RN + ' + CAST(N - 2 AS NVARCHAR(3)) + N') % (SELECT COUNT(*) FROM T)
    UNION ALL
    SELECT TOP (SELECT COUNT(*) / 2 FROM T) 
        Team, 
        RN, 
        RoundNum = ' + CAST(N AS NVARCHAR(3)) + N', 
        Match = ROW_NUMBER() OVER (ORDER BY CASE WHEN RN = 1 THEN 1 ELSE 0 END, (RN + ' + CAST(N - 2 AS NVARCHAR(3)) + N') % (SELECT COUNT(*) FROM T) DESC),
        Slot = 2
    FROM T
    ORDER BY CASE WHEN RN = 1 THEN 1 ELSE 0 END, (RN + ' + CAST(N - 2 AS NVARCHAR(3)) + N') % (SELECT COUNT(*) FROM T) DESC
) AS T
'
FROM (SELECT ROW_NUMBER() OVER (ORDER BY (SELECT NULL)) FROM sys.objects) T(N)
ORDER BY N;

SELECT @SQL = N'
WITH T AS 
(
    SELECT Team, RN = ROW_NUMBER() OVER (ORDER BY Team) 
    FROM dbo.Teams 
    UNION ALL 
    SELECT ''Bye'', COUNT(*) + 1 
    FROM dbo.Teams 
    HAVING COUNT(*) % 2 = 1
),
CTE2 AS 
(
' + STUFF(@SQL, 1, 11, '') + N'
)
SELECT T1.RoundNum, T1.Match, Team1 = T1.Team, Team2 = T2.Team
FROM
(
    SELECT *
    FROM CTE2
    WHERE Slot = 1
) AS T1 JOIN
(
    SELECT *
    FROM CTE2
    WHERE Slot = 2
) AS T2
    ON T2.RoundNum = T1.RoundNum
    AND T2.Match = T1.Match;';


EXEC sp_executesql @SQL;

基本上，它通过生根1并将所有团队转移到1来完成你的wiki链接中描述的fix one of the contributors in the first or last column of the table。对于奇数队，它会增加一个“再见”对手。它只是在表中循环N或N-1次（取决于是否有偶数或奇数的团队）。