Oracle SQL [1 .. *]关系|在[... *]中排序后，从[1 ...]中选择所有行，然后从[... *]中选择上一行。

Question

我想在过去2个月内select * from Table TRAINEE +前一个REPORT.DATE。

TRAINEE
+----+----------+
| ID | NAME     |   
+----+----------+   
| 1  | John Doe |
+----+----------+
| 2  | Jane Doe |
+----+----------+

REPORT
+------------+------------+---------------+
| TRAINEE_ID | DATE       | REPORT        |
+------------+------------+---------------+
| 1          | 01.07.2018 | Not Important |
+------------+------------+---------------+
| 1          | 02.07.2018 | Not Important |
+------------+------------+---------------+
| 1          | 03.07.2018 | Not Important |
+------------+------------+---------------+
| 2          | 02.07.2018 | Not Important |
+------------+------------+---------------+
| 2          | 02.07.2018 | Not Important |
+------------+------------+---------------+
| 2          | 03.07.2018 | Not Important |
+------------+------------+---------------+


Wanted results
+----+----------+--------------+
| ID | NAME     | FIRST_REPORT |
+----+----------+--------------+
| 1  | John Doe | 01.07.2018   |
+----+----------+--------------+
| 2  | Jane Doe | 02.07.2018   |
+----+----------+--------------+

我已经尝试过...

通过这种方式，我只给我一行带日期，其余的行用NULL填充，因为联接仅返回一行。删除ROWNUM过滤器将使我的查询为TRAINEE中发现的每一行返回一行REPORT。所以这也不行。我必须在哪里放置ROWNUM过滤器？

SELECT 
    TRAINEE.*, 
    OUTER_ORDER_DATE.DATE 
FROM
    Trainee
LEFT JOIN 
    (
    SELECT 
        DATE,
        ID,
        ROWNUM as rnum
    FROM 
        (
            SELECT 
                 DATE,
                 ID, 
              FROM 
                 REPORT INNER_ORDER_DATE 
             WHERE 
                 INNER_ORDER_DATE.DATE >= add_months(sysdate,-2)
             ORDER BY 
                 INNER_ORDER_DATE.DATE ASC
                                 )  
    WHERE 
        rnum < 2
        ) ON OUTER_ORDER_DATE ON OUTER_ORDER_DATE.ID = a.ID

然后，我尝试了以下查询，该查询的语法有些错误；内部查询无法访问外部查询的Trainee.ID。

SELECT 
    Trainee.*,
    (SELECT 
        DATE 
       FROM (
          SELECT 
               DATE 
            FROM 
               REPORT 
           WHERE
               ID = TRAINEE.ID 
             AND 
               DATE >= add_months(sysdate,-2)
           ORDER BY
               DATE ASC
                  ) 
      WHERE
          ROWNUM < 2
     ) as DATE
 FROM 
    TRAINEE

要使所需的结果在上方，我的查询应该是什么样的？

如果这个问题已经回答，请给我链接。我不知道如何搜索这种情况。谢谢。

Answer 1

您应该尝试使用以下代码：

SELECT trainee.id, trainee.name, report.report_date
  FROM trainee
       JOIN (  SELECT trainee_id, MIN (report_date) AS report_date
                 FROM report
                WHERE report_date >= ADD_MONTHS (SYSDATE, -2)
             GROUP BY trainee_id) report
           ON (report.trainee_id = trainee.id)

Answer 2

尝试一下：

select t.id, t.name, min(r.date) firstdate
from trainee t, report r
where t.id = r.id
and r.date >= add_months(sysdate,-2)