这是更新的问题：

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出现3次，但date不同。我想编写一个返回唯一value的查询，该查询具有最大date，如上表所示：

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

我怎么能这样做？

这是更新的问题：

我遇到的真正问题比上面的简化版本复杂一点。一旦我知道了简化版本的答案，我想我可以再向前迈进一步，但我的客人我错了。所以，我正在更新这里的问题。

我有两张表如下：

      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

此处，Table 1和Table 2由id2

加入

我想得到的是两条记录如下：

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安装程序：

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;

<强>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

<强>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;

<强>输出：

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

在这种情况下，如何更改我的sql以获得我想要的内容？

这是更新的问题：

3 个答案: