在这种情况下，我需要如何更改我的 sql 以获得我想要的？

Question

我有一张如下表：

id  value    date
1    5    2015-01-10
2    5    2015-06-13
3    5    2015-09-05
4    11   2015-02-11
5    11   2015-01-10
6    11   2015-01-25

可以看出，每个value 以不同的date 出现3 次。我想编写一个返回唯一values 的查询，该values 具有最大date，对于上表如下：

id  value    date
3    5    2015-09-05
4    11   2015-02-11

我该怎么做？

这是更新后的问题：

我遇到的真正问题比上面的简化版本要复杂一些。我以为一旦我知道了简化版的答案，我就可以更进一步，但我错了。所以，我在这里更新问题。

我有 2 个如下表：

      Table 1
id  id2    date
1    2   2015-01-10
2    5   2015-06-13
3    9   2015-09-05
4    10  2015-02-11
5    26  2015-01-10
6    65  2015-01-25

      Table 2
id  id2    data
1    2       A
2    5       A
3    9       A
4    10      B
5    26      B
6    65      B

这里，Table 1 和 Table 2 加入了 id2

我想要得到的是如下两条记录：

id2  date       data
9   2015-01-10    A
10  2015-02-11    B

Answer 1

您可以使用row_number 选择每个值的日期最长的行

select * from (
    select t2.id2, t1.date, t2.data, 
        row_number() over (partition by t2.data order by t1.date desc) rn
    from table1 t1
    join table2 t2 on t1.id = t2.id2
) t where rn = 1

Answer 2

select a.id, a.value, a.date
from mytable a,
   ( select id, max(date) maxdate
       from mytable b
     group by id) b
where a.id = b.id
  and a.date = b.maxdate;

Answer 3

Oracle 设置：

CREATE TABLE Table1 ( id, id2, "date" ) AS
SELECT 1,    2,   DATE '2015-01-10' FROM DUAL UNION ALL
SELECT 2,    5,   DATE '2015-06-13' FROM DUAL UNION ALL
SELECT 3,    9,   DATE '2015-09-05' FROM DUAL UNION ALL
SELECT 4,    10,  DATE '2015-02-11' FROM DUAL UNION ALL
SELECT 5,    26,  DATE '2015-01-10' FROM DUAL UNION ALL
SELECT 6,    65,  DATE '2015-01-25' FROM DUAL;

CREATE TABLE Table2 ( id, id2, data ) AS
SELECT 1,    2,       'A' FROM DUAL UNION ALL
SELECT 2,    5,       'A' FROM DUAL UNION ALL
SELECT 3,    9,       'A' FROM DUAL UNION ALL
SELECT 4,    10,      'B' FROM DUAL UNION ALL
SELECT 5,    26,      'B' FROM DUAL UNION ALL
SELECT 6,    65,      'B' FROM DUAL;

查询：

SELECT MAX( t1.id  ) KEEP ( DENSE_RANK LAST ORDER BY t1."date" ) AS id,
       MAX( t1.id2 ) KEEP ( DENSE_RANK LAST ORDER BY t1."date" ) AS id2,
       MAX( t1."date" ) AS "date",
       t2.data
FROM   Table1 t1
       INNER JOIN
       Table2 t2
       ON ( t1.id = t2.id AND t1.id2 = t2.id2 )
GROUP BY t2.data

输出：

        ID        ID2 date                DATA
---------- ---------- ------------------- ----
         3          9 2015-09-05 00:00:00 A    
         4         10 2015-02-11 00:00:00 B    

查询 2：

SELECT id,
       id2,
       "date",
       data
FROM   (
  SELECT t1.*,
         t2.data,
         ROW_NUMBER() OVER ( PARTITION BY t2.data ORDER BY t1."date" DESC ) AS rn
  FROM   Table1 t1
         INNER JOIN
         Table2 t2
         ON ( t1.id = t2.id AND t1.id2 = t2.id2 )
)
WHERE  rn = 1;

输出：

        ID        ID2 date                DATA
---------- ---------- ------------------- ----
         3          9 2015-09-05 00:00:00 A    
         4         10 2015-02-11 00:00:00 B