How to return the correct row of data using diffferent conditions?

Question

I am having some problems with an sql query and I hope someone can help please?
The data I am using is customers with multiple transactions. If a customer contains one transaction where the transaction type = 'W' then I need to set the output value to be transaction.ValueA. If the customer does not contain any transactions where the transaction type is 'W' then I need to set the output value to be
the most recent transaction.ValueB where transaction.transaction_date <= customer.cust_mod_date.
Here is an example of the data. For each test customer 10 and 20 I have put a star against the value I want to return
CUSTOMER_ID CUST_MOD_DATE TX_DATE      TX_TYPE TX_VALUEA TX_VALUEB
10          15/07/2009 16/07/2009     A     110      95
10          15/07/2009 14/07/2009     A     100      90(*)          
10          15/07/2009 13/07/2009     A     90          10
10          15/07/2009 12/07/2009     A     80          5
20          15/07/2009 15/07/2009     A     60          10
20          15/07/2009 14/07/2009     W     50(*)     20
20          15/07/2009 13/07/2009     A     40          30
ie
CREATE TABLE
TMP_CUSTOMER (CUSTOMER_ID NUMBER, CUST_MOD_DATE DATE);
insert into tmp_customer
values(10, to_date('15/07/2009','dd/mm/yyyy'));
insert into tmp_customer
values(20, to_date('15/07/2009','dd/mm/yyyy'));
CREATE TABLE
TMP_TRANSACTION (TX_ID NUMBER, CUSTOMER_ID NUMBER, TX_DATE DATE, TX_TYPE VARCHAR2(1), TX_VALUEA NUMBER, TX_VALUEB NUMBER);
INSERT INTO TMP_TRANSACTION
VALUES (1,10, to_date('16/07/2009','dd/mm/yyyy'),'A',110,95);
INSERT INTO TMP_TRANSACTION
VALUES (2,10, to_date('14/07/2009','dd/mm/yyyy'),'A',100,90);
INSERT INTO TMP_TRANSACTION
VALUES (3,10, to_date('13/07/2009','dd/mm/yyyy'),'A',90,10);
INSERT INTO TMP_TRANSACTION
VALUES (4,10, to_date('12/07/2009','dd/mm/yyyy'),'A',80,5);
INSERT INTO TMP_TRANSACTION
VALUES (5,20, to_date('15/07/2009','dd/mm/yyyy'),'A',60,10);
INSERT INTO TMP_TRANSACTION
VALUES (6,20, to_date('14/07/2009','dd/mm/yyyy'),'W',50,20);
INSERT INTO TMP_TRANSACTION
VALUES (7,20, to_date('13/07/2009','dd/mm/yyyy'),'A',40,30);
The query I have so far is
(SELECT CUSTOMER_ID, CUST_MOD_DATE, TX_DATE, TYPE_FLAG, TX_VALUEA, TX_VALUEB, RN
FROM (SELECT CUST.CUSTOMER_ID, CUST.CUST_MOD_DATE,TRANS.TX_DATE, TRANS.TYPE_FLAG, TRANS.TX_VALUEA,TRANS.TX_VALUEB,
ROW_NUMBER() OVER (partition BY TRANS.CUSTOMER_ID ORDER BY TRANS.TX_DATE DESC) RN
FROM TMP_CUSTOMER CUST,
--- Return all transactions creating a type_flag field where Y = type W, else N ---
SELECT CUST.CUSTOMER_ID, TX.TX_DATE, TX.TX_VALUEA, TX.TX_VALUEB, CUST.CUST_MOD_DATE, TX.TX_TYPE,
CASE WHEN NVL(TX.TX_TYPE,'0') <> 'W' THEN 'N'
WHEN NVL(TX.TX_TYPE,'0') = 'W' THEN 'Y'
ELSE 'N'
END AS TYPE_FLAG
FROM TMP_TRANSACTION TX, TMP_CUSTOMER CUST
WHERE TX.CUSTOMER_ID = CUST.CUSTOMER_ID
AND CUST.CUSTOMER_ID in
'10','20'
) TRANS
WHERE CUST.CUSTOMER_ID = TRANS.CUSTOMER_ID
--AND   TRANS.TX_DATE <= CUST.CUST_MOD_DATE
AND CUST.CUSTOMER_ID in
('10','20'
Can anyone please help with how I extract the record I am looking for
ie customer 10 has amount 90
customer 20 has amount 50.
Thanks :-)
GB

Answer 1

SQL> select c_id
  2  ,      cust_mod_date
  3  ,      tx_date
  4  ,      tx_type
  5  ,      tx_valuea
  6  ,      tx_valueb
  7  from ( select c.customer_id c_id
  8         ,      c.cust_mod_date
  9         ,      t.tx_date
10         ,      t.tx_type
11         ,      t.tx_valuea
12         ,      t.tx_valueb
13         ,      row_number() over (partition by c.customer_id order by t.customer_id, t.tx_date desc) rn
14         from   tmp_customer c
15         ,      tmp_transaction t
16         where  t.customer_id = c.customer_id     
17         and    t.tx_date <= c.cust_mod_date
18       )
19  where case
20          when tx_type = 'W' then 1
21          when rn = 1
22          and  not exists ( select null
23                            from   tmp_transaction t2
24                            where  t2.customer_id = c_id
25                            and    t2.tx_type = 'W'
26                          )
27          then 1
28        end = 1;
      C_ID CUST_MOD_ TX_DATE   T  TX_VALUEA  TX_VALUEB
        10 15-JUL-09 14-JUL-09 A        100         90
        20 15-JUL-09 14-JUL-09 W         50         20
2 rows selected.