SELECT子查询中的ORACLE ORDER BY

Question

I want to select a varchar field SUBJECT in a subquery, ordered by a date field DATETO. Specific: the ONE subject field of the latest entry, therefore ordered by the date field.

SELECT MDKAMVP.MDKAMDA_SID, 
(select SUBJECT from mdkndlst where rownum=1 and SUBJECT is not null 
order by DATETO) NAKTION, MDKAMVP.ROWID ROW_ID 
FROM SPRINGV2.MDKAMVP order by MDKAMVP.INDSTATUS

Error:

ORA-00907: Rechte Klammer fehlt
00907. 00000 -  "missing right parenthesis"
*Cause:    
*Action:
Fehler in Zeile: 8 Spalte: 99

It works without the order by DATETO

Answer 1

In Oracle 12c , you can use the new FETCH FIRST clause:

SELECT
    mdkamvp.mdkamda_sid,
    (SELECT subject
        FROM mdkndlst
        WHERE subject IS NOT NULL
        ORDER BY dateto
        FETCH FIRST 1 ROW ONLY) naktion,
    mdkamvp.rowid row_id
FROM springv2.mdkamvp
ORDER BY mdkamvp.indstatus

Answer 2

Assigning rownum to a row is done before applying ORDER BY clause, so this query

SELECT subject
FROM   mdkndlst
WHERE  rownum = 1
       AND subject IS NOT NULL
ORDER  BY dateto

in fact returns a random row. I believe this is not what you wanted. You probably wanted first to apply ORDER BY and then take the first row. That's where subqueries may come in handy:

SELECT subject
FROM   (SELECT subject
        FROM   mdkndlst
        WHERE  subject IS NOT NULL
        ORDER  BY dateto)
WHERE  rownum = 1

and such query you may now use as a scalar subquery

SELECT mdkamvp.mdkamda_sid
      ,(SELECT subject
        FROM   (SELECT subject
                FROM   mdkndlst
                WHERE  subject IS NOT NULL
                ORDER  BY dateto)
        WHERE  rownum = 1) naktion
      ,mdkamvp.rowid row_id
FROM   springv2.mdkamvp
ORDER  BY mdkamvp.indstatus

Answer 3

you should use first_value

SELECT mdkamvp.mdkamda_sid,

  (SELECT DISTINCT first_value(subject) over (partition BY subject
                                              ORDER BY dateto DESC)
   FROM mdkndlst
   WHERE subject IS NOT NULL ) naktion,
       mdkamvp.rowid row_id
FROM springv2.mdkamvp
ORDER BY mdkamvp.indstatus

Answer 4

Instead of using a scalar sub-query in the select list, use a derived table where you don't have the limitation with the order by:

SELECT MDKAMVP.MDKAMDA_SID, 
       x.subject as NAKTION, 
       MDKAMVP.ROWID ROW_ID 
FROM SPRINGV2.MDKAMVP 
  cross join (
    select SUBJECT 
    from mdkndlst 
    where rownum=1 
      and SUBJECT is not null 
    order by DATETO DESC
  ) x
order by MDKAMVP.INDSTATUS;

As the derived table is guaranteed to return exactly one row, the cross join will not change the overall result.

If you want the latest subject you should also order the DATETO descending. Without that you will get the oldest subject.

If you are using 12c then you might want to use the fetch first option as Jiri has shown.