Question

我正在尝试编写一个sql查询，显示两支球队相互比赛的频率。

Id | Team1 | Team2 | Date 
1  |   A   |   B   | 25/5/11
2  |   B   |   A   | 26/5/11
3  |   A   |   C   | 27/5/11
4  |   C   |   B   | 28/5/11
5  |   A   |   B   | 28/5/11

结果应为：

A vs B => 3
A vs C => 1
C vs B => 1

将A-B和B-A计为不同是一个简单的查询。但是我无法将它们统计在一起。

有什么建议吗？

Answer 1

我在分组之前使用了一个子查询来重新排序。

SELECT first_team, second_team, count(*)
FROM (
    SELECT 
        CASE WHEN Team1 < Team2 THEN Team1 ELSE Team2 END AS first_team,
        CASE WHEN Team1 < Team2 THEN Team2 ELSE Team1 END AS second_team
    FROM table
) a
GROUP BY first_team, second_team;

Answer 2

SELECT Team1, Team2, SUM(num) FROM (
   SELECT Team1, Team2, COUNT(*) num
   FROM table_name
   GROUP BY Team1, Team2
  UNION ALL
   SELECT Team2, Team1, COUNT(*) num
   FROM table_name
   GROUP BY Team2, Team1
) combined
WHERE Team1 < Team2
GROUP BY Team1, Team2

编辑：更新以在必要时撤消团队。

注意：这比使用CASE的版本运行速度要快得多，因为它会充分利用索引。

Edit2：使用索引移动到哪里更快。

Answer 3

SELECT 
  (CASE WHEN Team1<Team2 THEN Team1 ELSE Team2) Team1,
  (CASE WHEN Team1>Team2 THEN Team1 ELSE Team2) Team2,
  COUNT(*)  cnt
FROM <table> 
GROUP BY 
  (CASE WHEN Team1<Team2 THEN Team1 ELSE Team2) Team1,
  (CASE WHEN Team1>Team2 THEN Team1 ELSE Team2) Team2

Answer 4

实现目标的方法很少：

SELECT Teams, Games = COUNT(*) FROM 
(
  SELECT 
    Teams = CASE WHEN Team1 < Team2 THEN Team1 ELSE Team2 END + ' vs ' +
            CASE WHEN Team1 < Team2 THEN Team2 ELSE Team1 END
  FROM MY_TABLE 
) AS T
GROUP BY Teams

OR，如果您使用SQL 2005/2008

;WITH T AS (
  SELECT 
    Teams = CASE WHEN Team1 < Team2 THEN Team1 ELSE Team2 END + ' vs ' +
            CASE WHEN Team1 < Team2 THEN Team2 ELSE Team1 END
  FROM MY_TABLE 
)
SELECT Teams, Games = COUNT(*) FROM T GROUP BY Teams

以上两个都会给你相同的结果

/*
Teams     Games
-------|------
A vs B  3
A vs C  1
B vs C  1
*/

以下是您可以使用的脚本：

/* TEST DATA */
DECLARE @t AS TABLE ( ID INT, Team1 CHAR(1), Team2 CHAR(1), playdate [DATETIME] )
INSERT INTO @t (Team1 , Team2 , playdate)
          SELECT 'A' , 'B', '20110525'
UNION ALL SELECT 'B' , 'A', '20110526'    
UNION ALL SELECT 'A' , 'C', '20110527'    
UNION ALL SELECT 'C' , 'B', '20110528'    
UNION ALL SELECT 'A' , 'B', '20110528'    


/* STYLE 1 */    
;WITH T AS (
  SELECT 
    Teams = CASE WHEN Team1 < Team2 THEN Team1 ELSE Team2 END + ' vs ' +
            CASE WHEN Team1 < Team2 THEN Team2 ELSE Team1 END
  FROM @t 
)
SELECT Teams, Games = COUNT(*) FROM T GROUP BY Teams

/* STYLE 2 */
SELECT Teams, Games = COUNT(*) FROM 
(
  SELECT 
    Teams = CASE WHEN Team1 < Team2 THEN Team1 ELSE Team2 END + ' vs ' +
            CASE WHEN Team1 < Team2 THEN Team2 ELSE Team1 END
  FROM @t 
) AS T
GROUP BY Teams

/ * OR，使用它来切换列* /

/* STYLE 3 */    
;WITH T AS (
  SELECT 
      Team1 = CASE WHEN Team1 < Team2 THEN Team1 ELSE Team2 END 
    , Team2 = CASE WHEN Team1 < Team2 THEN Team2 ELSE Team1 END
  FROM @t 
)
SELECT Team1 , Team2, Games = COUNT(*) FROM T GROUP BY Team1 , Team2

/* STYLE 4 */
SELECT Team1 , Team2, Games = COUNT(*) FROM 
(
  SELECT 
      Team1 = CASE WHEN Team1 < Team2 THEN Team1 ELSE Team2 END 
    , Team2 = CASE WHEN Team1 < Team2 THEN Team2 ELSE Team1 END
  FROM @t 
) AS T
GROUP BY Team1 , Team2

如何查询超过2列的计数

4 个答案: