How to add a dummy row in the result set of a SELECT statement.

Question

Hello Everyone -
I have requirment to add a dummy row in the result set of a SELECT statement.
For e.g. lets say there is a table Payment having following colums:
Payment_id number
status varchar2(10)
amount number
payment_date date
so here is the data :-
Payment_id Status Amount payment_date
1 Applied 100 12/07/2008
2 Reversed 200 01/ 06/2009
3 Applied 300 01/ 07/2009
Here is my SQL
Select * form payment where payment_date >= 01/01/2009
Output will be
2 Reversed 200 01/ 06/2009
3 Applied 300 01/ 07/2009
My desired output is below
2 Reversed 200 01/ 06/2009
3 Applied 300 01/ 07/2009
2 Reversed -200 01/ 06/2009 ------(Dummy Row)
Thrid row here is the dummy row which I want to add when status is "Reversed"
I would be very thankful for any kind of help in this regard ...
Thanks,
Gaurav

Answer 1

Cartesion joining against a dummy table is a useful method of creating a dummy row:
with my_tab as (select 1 cust_id, 1 Payment_id, 'Applied' Status, 100 Amount, to_date('12/07/2008', 'mm/dd/yyyy') payment_date from dual union all
                select 1 cust_id, 2 Payment_id, 'Reversed' Status, 200 Amount, to_date('01/06/2009', 'mm/dd/yyyy') payment_date from dual union all
                select 1 cust_id, 3 Payment_id, 'Applied' Status, 300 Amount, to_date('01/06/2009', 'mm/dd/yyyy') payment_date from dual union all
                select 2 cust_id, 1 Payment_id, 'Applied' Status, 100 Amount, to_date('12/07/2008', 'mm/dd/yyyy') payment_date from dual union all
                select 2 cust_id, 2 Payment_id, 'Reversed' Status, 200 Amount, to_date('01/05/2009', 'mm/dd/yyyy') payment_date from dual union all
                select 2 cust_id, 3 Payment_id, 'Applied' Status, 300 Amount, to_date('01/06/2009', 'mm/dd/yyyy') payment_date from dual union all
                select 2 cust_id, 4 Payment_id, 'Reversed' Status, -400 Amount, to_date('01/06/2009', 'mm/dd/yyyy') payment_date from dual union all
                select 2 cust_id, 5 Payment_id, 'Applied' Status, 500 Amount, to_date('01/07/2009', 'mm/dd/yyyy') payment_date from dual),
                --- end of mimicking your table
      dummy as (select 'Reversed' col1, 1 rn from dual union all
                select 'Reversed' col1, 2 rn from dual)
select mt.cust_id,
       mt.payment_id,
       mt.status,
       decode(dummy.rn, 2, -1*mt.amount, mt.amount) amount,
       mt.payment_date
from   my_tab mt,
       dummy
where  mt.status = dummy.col1 (+)
order by mt.cust_id, mt.payment_id, dummy.rn nulls first;
CUST_ID     PAYMENT_ID     STATUS     AMOUNT     PAYMENT_DATE
1     1     Applied     100     07/12/2008
1     2     Reversed     200     06/01/2009
1     2     Reversed     -200     06/01/2009
1     3     Applied     300     06/01/2009
2     1     Applied     100     07/12/2008
2     2     Reversed     200     05/01/2009
2     2     Reversed     -200     05/01/2009
2     3     Applied     300     06/01/2009
2     4     Reversed     -400     06/01/2009
2     4     Reversed     400     06/01/2009
2     5     Applied     500     07/01/2009Edited by: Boneist on 07-Jan-2009 23:10
NB. You may have to mess around with the ordering if that's not come back in the order you wanted. You didn't mention what the rules were for any expected ordering though, so I've made up my own *{;-)
Also, I added an identifier (cust_id) to differentiate between different sets of payments, since that's usually the case. Remove that if it's not applicable for your case.