Performance issue with ORDER BY

Question

The following query runs in 60 milli sec with no order by clause. With order by it takes about 3 sec. The end result of the query is 25 records. One thing we noticed is order by is taking place after the union irrespective where we place the order by clause. Not sure how to make oracle perform order by on end result. Any thoughts truly appreciated.
SELECT *
FROM
(SELECT ROWNUM as R,
STATUS,
TASK_ID,
PRIORITY,
INSTALL_TYPE,
CUSTOMER_TYPE,
TYPE_ID,
QUEUE,
FALLOUTREASON,
START_DT,
NOTIF_CREATE_DT,
ACCT_NUM,
ADSLTN,
SDPID,
PERFORMER_DN,
SUPERVISOR_DN
FROM
(SELECT *
FROM
(SELECT *
FROM
(SELECT t.STATUS,
TASK_ID,
PRIORITY,
INSTALL_TYPE,
CUSTOMER_TYPE,
S.TYPE_ID,
QUEUE,
null FALLOUTREASON,
START_DT,
null NOTIF_CREATE_DT,
null ACCT_NUM,
ADSLTN,
null SDPID,
PERFORMER_DN,
SUPERVISOR_DN
FROM (select * from TASK_ACTIVITY where TYPE_ID='2' AND SUB_TYPE_ID='2' AND status not in ( 'Terminated','Complete') ) T,
SOEG_CRM S
WHERE t.activity_id= s.activity_id
UNION ALL
(SELECT t.STATUS,
TASK_ID,
PRIORITY,
null INSTALL_TYPE,
null CUSTOMER_TYPE,
TYPE_ID,
QUEUE,
'Review Letters for Printing' FALLOUT_REASON,
START_DT,
null NOTIF_CREATE_DT,
null ACCT_NUM,
null ADSLTN,
null SDPID,
PERFORMER_DN,
SUPERVISOR_DN
FROM (select * from TASK_ACTIVITY where TYPE_ID='3' AND status not in ( 'Terminated','Complete') ) T
UNION ALL
(SELECT t.STATUS,
TASK_ID,
PRIORITY,
INSTALL_TYPE,
CUSTOMER_TYPE,
op.TYPE_ID,
QUEUE,
FALLOUT_REASON,
START_DT,
NOTIF_CREATE_DT,
ACCT_NUM,
ADSLTN,
SDPID,
PERFORMER_DN,
SUPERVISOR_DN
FROM (select * from TASK_ACTIVITY where TYPE_ID='1' AND SUB_TYPE_ID='1' and status not in ( 'Terminated','Complete') ) T,
OPNOTES OP
WHERE t.activity_id= op.activity_id
UNION ALL
(SELECT t.STATUS,
TASK_ID,
PRIORITY,
INSTALL_TYPE,
CUSTOMER_TYPE,
a.TYPE_ID,
QUEUE,
null FALLOUTREASON,
START_DT,
null NOTIF_CREATE_DT,
null ACCT_NUM ,
ADSLTN,
null SDPID,
PERFORMER_DN,
SUPERVISOR_DN
FROM (select * from TASK_ACTIVITY where TYPE_ID='2' AND SUB_TYPE_ID='1' and status not in ( 'Terminated','Complete') ) T,
AELERA a
WHERE t.activity_id= a.activity_id
WHERE (PERFORMER_DN = 'cadmin1'
OR SUPERVISOR_DN in ('Address_Issues','PROCESSED','SG_EOSN','Test_Queue','Test_Queue_P','BUTST1','BUTST2','BU_UNAS','DATAR','PST','PST_ME','SVC','SVC_EX','SVC_ME','TEST_2_LETTER_QUEUE','TEST_2_OP_ESC_QUEUE','TEST_2_PROV_ESC_QUEUE','TEST_3','Test_4','Test_6','Test_8','test_5_LETTER_QUEUE','test_5_OP_ESC_QUEUE','test_5_PROV_ESC_QUEUE','cadmin1'))
AND ((STATUS = 'Pending'
AND PERFORMER_DN = QUEUE)
OR STATUS = 'Suspended'
OR STATUS = 'Acquired'
OR (STATUS = 'Pending'
AND PERFORMER_DN <> QUEUE))
AND (TYPE_ID = '2'
OR TYPE_ID = '3')
--order by priority
WHERE R >= 1
and R < 26
          --order by priority 
Here is the explain plan
19 SELECT STATEMENT
18 . VIEW
17 SORT [ORDER BY]
16 COUNT
15 . VIEW
14 UNION-ALL
4 NESTED LOOPS
1 APPL.TASK_ACTIVITY TABLE ACCESS [FULL]
3 APPL.SOEG_CRM TABLE ACCESS [BY INDEX ROWID]
2 APPL.XPK_SOEG_CRM INDEX [UNIQUE SCAN]
5 APPL.TASK_ACTIVITY TABLE ACCESS [FULL]
9 NESTED LOOPS
6 APPL.BSOMS_OPNOTES TABLE ACCESS [FULL]
8 APPL.TASK_ACTIVITY TABLE ACCESS [BY INDEX ROWID]
7 APPL.XPKTASK_ACTIVITY INDEX [UNIQUE SCAN]
13 NESTED LOOPS
10 APPL.TASK_ACTIVITY TABLE ACCESS [FULL]
12 APPL.AELERA TABLE ACCESS [BY INDEX ROWID]
11 APPL.XPK_AELERA INDEX [UNIQUE SCAN]

Answer 1

Hi,
I must admit, that I didn't read your whole query, but did you try to use a subselect?
Select a.* from (your_query) a
order by a.priorityBTW: Don't use SELECT *
Dim