Question

我有以下情况：我想使用tableB的评分更新tableA。挑战是：收视率随机变化，当更新tableB的记录时，我考虑了比赛的日期，如果评级发生变化，让我们在星期二说，比赛是在星期一之前，我希望评级为以前的评级不是最新评分。

#table A: contains rating of players, changes randomly at any date depending
#on drop of form from the players  

PID| Rating | DateChange  |
1  |    2   | 10-May-2014 |
1  |    4   | 20-May-2015 |
1  |   20   | 1-June-2015 |
2  |    4   | 1-April-2014|
3  |    4   | 5-April-2014|
2  |    3   | 3-May-2015  |

#Table B: contains match sheets. Every player has a different match sheet
#and plays different dates.

MsID | PID  | MatchDate    | Win | Rating |
 1   |  2   | 10-May-2014  |  No |    0   |
 2   |  1   | 15-May-2015  | Yes |    0   |
 3   |  3   | 10-Apr-2014  |  No |    0   |
 4   |  1   | 21-Apr-2015  | Yes |    0   |
 5   |  1   | 3-June-2015  | Yes |    0   |
 6   |  2   | 5-May-2015   |  No |    0   |

#I am trying to achieve this by running the ms-access query: i want to get
#every players rating at the time the match was played not his current
#rating. 

MsID | PID  | MatchDate    | Rating |
 1   |  2   | 10-May-2014  |    4   |
 2   |  1   | 15-May-2015  |    2   |
 3   |  3   | 10-Apr-2014  |    4   |
 4   |  1   | 21-Apr-2015  |    2   |
 5   |  1   | 3-June-2015  |    20  |
 6   |  2   | 5-May-2015   |    3   |

我尝试了以下代码：

Update [B-table] as wdev
set wdev.rating = ( SELECT B.MsID, B.PID, B.MatchDate, A.rating as Rating 
FROM [B-table] B
INNER JOIN [A-table] A
  on B.PID = A.PID
INNER JOIN (     
  SELECT MAX(Y.DateChange) MDC, Y.PID, Z.Matchdate
  FROM [B-table] Z
  INNER Join [A-table] Y
   on Z.PID = Y.PID
  and Y.DateChange <= Z.MatchDate
  GROUP BY Y.PID, Z.Matchdate) C
  on C.mdc = A.DateChange
 and A.PID = C.PId
 and B.MatchDate = C.Matchdate) And B.MsID = Wdev.MsID

SQLFiddle with database schema

总结：我希望评分对应于匹配日期或之前的最大日期更改。

Answer 1

我认为你只想要一个相关的子查询：

update [B-table] as b
    set rating = (select top 1 rating
                  from [A-table] as a
                  where a.pid = b.pid and
                        a.datechange <= b.matchdate
                  order by a.datechange desc
                 ) ;

注意：由于MS Access处理top的方式，子查询可以在出现平局时返回多行。对此的正常解决方案是在order by中包含一个额外的键值，以防止绑定。但是，“a”表中似乎没有唯一的键。

使用ms-access中的sql使用另一个表中的最大日期和值更新表

SQLFiddle with database schema

1 个答案: