Trying to optimize this simple query

Question

Hi,
I am trying to optimize this simple query but the two methods I am trying actually make things worse.
The original query is:
SELECT customer_number, customer_name
FROM bsc_pdt_account_mv
where rownum <= 100
AND Upper(customer_name) like '%SP%'
AND customer_id IN
SELECT cust_id FROM bsc_pdt_assoc_sales_force_mv
WHERE area_identifier IN (
SELECT area_identifier FROM bsc_pdt_assoc_sales_force_mv
WHERE ad_identifier = '90004918' or rm_identifier = '90004918' or tm_identifier = '90004918'
The result set of this query returns me the first 100 rows in 88 seconds and they are all distinct by default (don't know why they are distinct).
My first attempt was to try to use table joins instead of the IN conditions:
SELECT
distinct -- A: I need to use distinct now
customer_number, customer_name
FROM bsc_pdt_account_mv pdt,
bsc_pdt_assoc_sales_force_mv asf,
SELECT distinct area_identifier FROM bsc_pdt_assoc_sales_force_mv
WHERE ad_identifier = '90004918' or rm_identifier = '90004918' or tm_identifier = '90004918'
) area
where
area.area_identifier = asf.area_identifier
AND asf.cust_id = pdt.customer_id
AND Upper(customer_name) like '%SP%'
AND rownum <= 100 -- B: strange when I comment this out
order by 1
I dont understand two things with this query. First issue, I now need to put in the distinct because the result set is not distinct by default. Second issue (very strange), when I put the rownum condition (<100) I get two rows in 1.5 seconds. If I remove the condition, I get 354 rows (whole result set) in 326 seconds.
My second attempt was to use EXISTS instead of IN:
SELECT
customer_number, customer_name
FROM bsc_pdt_account_mv pdt
where Upper(customer_name) like '%SP%'
AND rownum <= 100
AND EXISTS
select 1 from
bsc_pdt_assoc_sales_force_mv asf,
SELECT distinct area_identifier FROM bsc_pdt_assoc_sales_force_mv
WHERE ad_identifier = '90004918' or rm_identifier = '90004918' or tm_identifier = '90004918'
) area
where
area.area_identifier = asf.area_identifier
AND asf.cust_id = pdt.customer_id
This query returns a similar distinct result set as teh original one but takes pretty much the same time (87 seconds).

Answer 1

The query below hangs when run in TOAD or PL/SQL Dev. I noticed there is no rows returned from the inner table for this condition.
SELECT customer_number, customer_name
FROM
bsc_pdt_account_mv pdt_account
where rownum <= 100
AND exists (
SELECT pdt_sales_force.cust_id
FROM bsc_pdt_assoc_sales_force_mv pdt_sales_force
WHERE pdt_account.customer_id = pdt_sales_force.cust_id
AND (pdt_sales_force.rm_identifier = '90007761' or pdt_sales_force.tm_identifier = '90007761') )
ORDER BY customer_name
-- No rows returned by this query
SELECT pdt_sales_force.cust_id
FROM bsc_pdt_assoc_sales_force_mv pdt_sales_force
WHERE pdt_sales_force.rm_identifier = '90007761' or pdt_sales_force.tm_identifier = '90007761'