Oracle SQL [1..*] Relation | Select all rows from [1…] + top-row from […*] after order by in […*]

Question

I want to select * from Table TRAINEE + the first REPORT.DATE within the last 2 months.

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   |
+----+----------+--------------+

I have tried...

This way gave me only one row with a date, rest filled with NULL , because the join only returns one row. Removing the ROWNUM filter will make my query return one row of TRAINEE for each row found in REPORT . So this wouldn't work as well. Where do I have to put the ROWNUM filter?

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

I then tried the following query, that has some wrong syntax; the inner query cannot access the outer query's 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

What does my query has to look like, to get the wanted result above?

If this question was answered already please link it for me. I have no idea how I could search for this scenario. Thank you.

Answer 1

You should try using this code:

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

Try this:

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)