* COUNT 1 *
select distinct count (CUSTOMER_ID) from DEMO_CUSTOMERS;

* COUNT 2 *
select count (CUSTOMER_ID)
   from DEMO_CUSTOMERS
where instr(upper(CUST_LAST_NAME), upper  ( nvl (:P1_CUST_LAST_NAME,CUST_LAST_NAME))) > 0

AND instr(upper(CUST_FIRST_NAME), upper  ( nvl (:P1_CUST_FIRST_NAME,CUST_FIRST_NAME))) > 0

order by 1

* COUNT 3 *

select count (*) from (
select CUSTOMER_ID, Initcap( CUST_LAST_NAME ||','|| CUST_FIRST_NAME   ) Name, 
CUST_CITY, CREDIT_LIMIT, CUST_EMAIL, NLS_TERRITORY,
case ACCOUNT_MGR_ID
  when   1 then 'John'
    when   2 then  'Bill'
    when 3 then 'Smith'
   when  4 then 'Joe'
        when 5 then 'Ron' else
         'N/A'
         end as MGR_id
   from DEMO_CUSTOMERS
where instr(upper(CUST_LAST_NAME), upper  ( nvl (:P1_CUST_LAST_NAME,CUST_LAST_NAME))) > 0

AND instr(upper(CUST_FIRST_NAME), upper  ( nvl (:P1_CUST_FIRST_NAME,CUST_FIRST_NAME))) > 0

order by 1)
where (
 instr(upper("NAME"),upper(nvl(:P1_SEARCH,"NAME"))) > 0  or
 instr(upper("CUST_CITY"),upper(nvl(:P1_SEARCH,"CUST_CITY"))) > 0  or
 instr(upper("CUST_EMAIL"),upper(nvl(:P1_SEARCH,"CUST_EMAIL"))) > 0  or
 instr(upper("NLS_TERRITORY"),upper(nvl(:P1_SEARCH,"NLS_TERRITORY"))) > 0  or
 instr(upper("MGR_ID"),upper(nvl(:P1_SEARCH,"MGR_ID"))) > 0
)