获取 MS Access 中每列的最新值

Question

请考虑 MS Access 中的此表：

Id       Year       Month         F1         F2         F3         F4
----------------------------------------------------------------------
1        2020         1           A          B          1          2
1        2020         2           AA      
1        2020         3                      BB         11
2        2020         1                                 3          4
2        2020         2           F          G 

我想要这样的结果：

Id       F1         F2         F3         F4
-----------------------------------------------
1        AA         BB         11         2
2        F          G          3          4

我想要每一列中的最新值，并将它们合并到每一行中

Id

。

如何使用 MS Access 中的查询获得此结果。

Answer 1

SELECT
    Id,
    (SELECT TOP 1 F1 FROM test t1 WHERE t1.Id = t.Id AND F1 IS NOT NULL ORDER BY [Year] DESC, [Month] DESC) AS F1,
    (SELECT TOP 1 F2 FROM test t1 WHERE t1.Id = t.Id AND F2 IS NOT NULL ORDER BY [Year] DESC, [Month] DESC) AS F2,
    (SELECT TOP 1 F3 FROM test t1 WHERE t1.Id = t.Id AND F3 IS NOT NULL ORDER BY [Year] DESC, [Month] DESC) AS F3,
    (SELECT TOP 1 F4 FROM test t1 WHERE t1.Id = t.Id AND F4 IS NOT NULL ORDER BY [Year] DESC, [Month] DESC) AS F4
FROM (
    SELECT DISTINCT Id 
    FROM test
) t

如果示例中的空单元格是空字符串而不是 NULL，则子查询中的条件将为

F1 <> "

。