Question

我想返回特定ID的最大值日期。看看这张表。

ID       Date       Value 
___      ____       _____
4545     9/17/12    5
4545     9/16/12    100
4545     9/15/12    20
2121     9/16/12    12
2121     9/15/12    132
2121     9/14/12    4
9999     9/16/12    45
9512     9/15/12    128
9512     9/14/12    323
2002     9/17/12    45

结果应该是：

ID       Date       Value 
___      ____       _____ 
4545     9/16/12    100       date for ID(4545) for max value(100)  is "9/16/12"
2121     9/15/12    132       date for ID(2121) for max value1(32)  is "9/15/12"
9999     9/16/12    45        date for ID(9999) for max value(45)   is "9/16/12"
9512     9/14/12    323       -||-
2002     9/17/12    45        -||-

我如何得到这个日期？

Answer 1

假设您正在使用SQL，您应该尝试这样的事情（这是MS SQL语法）：

SELECT [ID], [Date], [Value]
FROM [YourTable] AS [SRC]
WHERE NOT EXISTS (SELECT *
                  FROM [YourTable] AS [OTHER]
                  WHERE [OTHER].[ID] = [SRC].[ID] AND [OTHER].[Date] > [SRC].[Date])

这可能不是最有效的方法，但它应该有用......

Answer 2

计算ID的集合及其最大值，然后将其与原始集合相交。

SELECT * FROM t
JOIN (SELECT id, MAX(value) AS value FROM t GROUP BY id) AS max_t
USING (id, value)

返回特定id的最大值的日期

2 个答案: