Sql 艺术日期。我想把一些问题简化到能够提出一个合理的问题是相当困难的。我猜您已经更改了一些内容，因为USER甚至不是有效的列名，因为它是一个保留字。您好。我认为你的是对的。实际上，srinu的选项非常快，但我没有时间根据自己的需要正确地实现它。还有，这里有更多

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艺术日期。我想把一些问题简化到能够提出一个合理的问题是相当困难的。我猜您已经更改了一些内容，因为

USER

甚至不是有效的列名，因为它是一个保留字。您好。我认为你的是对的。实际上，srinu的选项非常快，但我没有时间根据自己的需要正确地实现它。还有，这里有更多的人发布与你相同的答案，但你有更好的解释。谢谢@菲利波-刚刚看了一下斯里努的答案。我们的两个答案应该给出大致相同的结果，并且在性能方面应该相似。

densite_-RANK

ad

ROW_-NUMBER

之间的区别在于，行号将是严格唯一的。例如，如果给定用户的两行具有相同的结束日期（我猜您不应该这样做），则

ROW\u NUMBER

将对这些1和2进行编号（可能是不确定的），但

densite\u RANK

将对它们进行编号，并返回两个。我认为，

首先为空

是必要的，因为它会从当前计划中产生。。这确实很快，但让我研究了稠密的东西。你介意再详细说明一下你在这里做了什么吗？（很抱歉这么生疏！）谢谢在

ORDER BY

子句中添加

NULLS FIRST

，可能会让它更清晰。不应该

sequen

严格地<2？@APC，太糟糕了，小伙子。请注意，我在谷歌上搜索。不明白为什么在简短的回答中询问细节会得到如此粗鲁的反馈。谢谢。这和米凯比克里基说的差不多。他只是得到了一个更长的解释。

USER |  PLAN |  START_DATE  |   END_DATE
1    |  A    |  20110101    |   NULL
1    |  B    |  20100101    |   20101231
2    |  A    |  20100101    |   20100505

select  plan
from    (
        select  plan
        from    YourTable
        where   User = 1
        order by
                case when end_date is null then '99991231' else end_date end desc
        )
where   rownum < 2

SELECT User, Plan, start_Date, MAX(End_Date) FROM Plans WHERE User NOT IN 
(SELECT User FROM Plans WHERE End_Date IS NULL)
GROUP BY Start_Date, Plan, User  
UNION  
SELECT User,Plan,Start_Date FROM Plans WHERE End_Date IS NULL

SELECT U.user 
,(SELECT Plan FROM t WHERE t.user=u.user AND end_date IS NULL LIMIT 1) AS Current_Plan
,(SELECT Plan FROM t WHERE t.user=u.user AND end_date IS NOT NULL ORDER BY end_date DESC LIMIT 1) AS Last_Plan
FROM 
( SELECT DISTINCT USER FROM t ) AS U

select PLAN
from USER_TABLE
where END_DATE is null or END_DATE = (
        select max(END_DATE)
        from USER_TABLE
        where USER = 1 and END_DATE is not null)
    and USER = 1

select user, plan, start_date, end_date
from (
  select 
    user, 
    plan, 
    start_date, 
    end_date, 
    row_number() over (partition by user order start_date desc) as row_num_1,
    row_number() over (partition by user order end_date desc nulls first) as row_num_2
  from user_table
  where user = :userid
)
where row_num_1 = 1

select user, plan, start_date, end_date
from (
  select 
    user, 
    plan, 
    start_date, 
    end_date, 
  from user_table
  where user = :userid
  order by start_date desc
)
where rownum = 1

SELECT user,plan,end_date,start_date 
FROM ( SELECT users,plans,end_date,start_date, DENSE_RANK() OVER ( PARTITION BY user 
                                                                   ORDER BY end_date DESC) sequen 
        FROM table_name 
     ) 
WHERE sequen <= 2

CREATE TABLE XY
( USERID      INTEGER                 NOT NULL
, PLAN        VARCHAR2(8)             NOT NULL
, START_DATE  DATE                    NOT NULL
, END_DATE    DATE                    )
  TABLESPACE USERS;


INSERT INTO XY ( USERID, PLAN, START_DATE, END_DATE )
       VALUES ( 1, 'A', To_Date('22-05-2011 00:00:00', 'DD-MM-YYYY HH24:MI:SS'), To_Date('22-05-2011 00:00:00', 'DD-MM-YYYY HH24:MI:SS') );
INSERT INTO XY ( USERID, PLAN, START_DATE, END_DATE )
       VALUES ( 1, 'B', To_Date('01-04-2011 00:00:00', 'DD-MM-YYYY HH24:MI:SS'), NULL );
INSERT INTO XY ( USERID, PLAN, START_DATE, END_DATE )
       VALUES ( 2, 'A', To_Date('03-05-2011 00:00:00', 'DD-MM-YYYY HH24:MI:SS'), To_Date('04-05-2011 00:00:00', 'DD-MM-YYYY HH24:MI:SS') );
INSERT INTO XY ( USERID, PLAN, START_DATE, END_DATE )
       VALUES ( 2, 'B', To_Date('15-05-2011 00:00:00', 'DD-MM-YYYY HH24:MI:SS'), To_Date('20-05-2011 00:00:00', 'DD-MM-YYYY HH24:MI:SS') );
COMMIT WORK;

SELECT USERID, PLAN, END_DATE, START_DATE
  FROM (SELECT USERID,
               PLAN,
               END_DATE,
               START_DATE,
               ROW_NUMBER() OVER(PARTITION BY USERID ORDER BY END_DATE DESC) SEQUEN
          FROM XY)
 WHERE SEQUEN < 2

with t as 
(select 1 as col_id, 1 as USER_id, 'A' as PLAN , 20110101 as START_DATE, NULL as  END_DATE from dual union all
 select 2,1,'B', 20100101,20101231 from dual union all
 select 3,2,'A', 20100102,20100505 from dual union all
 select 4,2,'C', 20100101,20100102 from dual)
--
SELECT user_id, plan
  FROM (SELECT user_id,
               plan,
               MAX(nvl(END_DATE, 99999999)) over(PARTITION BY user_id) max_date,
               nvl(END_DATE, 99999999) END_DATE
          FROM t)
 WHERE max_date = end_date