Using ORDER BY in UNION clause in cursor

Question

Hi Everybody,
I have one situation and i need your help guys. I have to use ORDER BY in UNION of two queries and return value in cursor.
OPEN cursor FOR
SELECT ID, DESC,SID, ITID, SID_DESC
FROM (SELECT A.ID,
A.DESC,
B.SID,
NULL AS ITID,
B.SID_DESC
FROM TABLEA A, TABLEB B
WHERE A.ID = B.ID
order by A.SORTORDER asc,B.SORTORDER)
UNION
SELECT ID, DESC, ,SID,ITID, ITID_DESCRIPTION,
FROM (SELECT A.ID,
A.DESC,
NULL AS SID,
C.ITID,
C.ITID_DESC,
FROM TABLEA A,
TABLEC C
WHERE A.ID = C.ID
order by A.SORTORDER asc,C.SORTORDER)
I SORT ORDER is column in all three tables. TABLEA has unique number for each record as sort order. TABLEB has sortorder as 1 for each id. If id is two times then its 1 and 2 for each id. TABLEC has sort order as TABLEB, 1 for each id and if id is two times then it is 1 and 2 and id id is three times, it is 1, 2, 3.
I am not getting correct sorting as i cant use order by like this in UNION. Please let me know how i can handle this.
Thank you in advance to everybody.
I will really appreciate your comments and responses.

Answer 1

Hi,
You can use ORDER BY in a sub-query, but there's usually no point in doing so, because the super-query won't necessarily preserve that order. You need to make the columns that you want to ORDER BY available to the main query, so that they can be used there.
Try this:
SELECT      ID, DESC,SID, ITID, SID_DESC
FROM      (
         SELECT    A1.ID,
                    A1.DESC,
                B.SID,
                NULL          AS ITID,
                B.SID_DESC,
                A1.SORTORDER     AS sortorder_1
                B.SORTORDER     AS sortorder_2
         FROM      TABLEA     A1,
                    TABLEB     B
         WHERE     A1.ID = B.ID
    UNION
         SELECT    A2.ID,
                    A2.DESC,
                NULL          AS SID,
                       C.ITID,
                C.ITID_DESC,
                A2.SORTORDER     AS sortorder_1
                B.SORTORDER     AS sortorder_2
         FROM      TABLEA          A2,
                    TABLEC         C
         WHERE     A2.ID = C.ID
order by  SORTORDER_1     ASC     -- ASC is the default, but it doesn't hurt to say it
       SORTORDER_2This assumes that tableb.sortorder and tablec.sortorder have the same, or at least similar, data types. If not, explicitly convert sortorder_1 in one branch of the UNION to the type of sortorder_2 in the other branch.
Using the same alias to mean different things in the same query is just asking for trouble. I changed the table alias a (which was used in different places to mean two different things) to A1 and A2, each of which means only one thing.
I hope this answers your question.
If not, post a little sample data (CREATE TABLE and INSERT statements, relevant columns only) for all tables, and also post the results you want from that data.
Explain, using specific examples, how you get those results from that data.
Always say which version of Oracle you're using.