how to speed up the order by query in oracle - oracle

Question

my below pagination query runs faster (2.5 sec) without order by .
if I use order by it get slower (180 sec).
Total number of record is only 90000
select * from(
select i.*,rownum rno from (
select opp.updat,nvl(s.name,c.vemail),s.name,c.vemail
from sfa_opportunities opp,sfa_company s, customer c
where opp.companyid = c.companyid(+)
and opp.custid = c.custid(+)
and opp.companyid = s.companyid(+)
and opp.sfacompid = s.sfacompid(+)
order by 2 asc, 1 asc
)i) where rno >= 1 and rno <= 30
I have given the explain plan below for reference.
---------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes |TempSpc| Cost (%CPU)| Time |
---------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 97980 | 110M| | 14137 (1)| 00:03:18 |
|* 1 | VIEW | | 97980 | 110M| | 14137 (1)| 00:03:18 |
| 2 | COUNT | | | | | | |
| 3 | VIEW | | 97980 | 109M| | 14137 (1)| 00:03:18 |
| 4 | SORT ORDER BY | | 97980 | 6602K| 15M| 14137 (1)| 00:03:18 |
| 5 | NESTED LOOPS OUTER | | 97980 | 6602K| | 13137 (1)| 00:03:04 |
|* 6 | HASH JOIN RIGHT OUTER | | 97980 | 3635K| 1136K| 614 (1)| 00:00:09 |
| 7 | TABLE ACCESS FULL | SFA_COMPANY | 34851 | 714K| | 58 (0)| 00:00:01 |
| 8 | TABLE ACCESS FULL | SFA_OPPORTUNITIES | 97980 | 1626K| | 390 (1)| 00:00:06 |
|* 9 | TABLE ACCESS BY INDEX ROWID| CUSTOMER | 1 | 31 | | 1 (0)| 00:00:01 |
|* 10 | INDEX UNIQUE SCAN | PK_CUSTOMER_CUSTID | 1 | | | 1 (0)| 00:00:01 |
---------------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter("RNO"<=30 AND "RNO">=1)
6 - access("OPP"."COMPANYID"="S"."COMPANYID"(+) AND "OPP"."SFACOMPID"="S"."SFACOMPID"(+))
9 - filter("OPP"."COMPANYID"="C"."COMPANYID"(+))
10 - access("OPP"."CUSTID"="C"."CUSTID"(+))

Answer 1

You're sorting on nvl(s.name,c.vemail), then opp.updat. My guess is the NVL may prevent a lot of optimization, because Oracle can't tell what the value of that column is going to be without looking at every row in the joined result. You could try adding indexes on those three columns or a function based index on nvl(s.name,c.vemail).