Help needed in writing SQL CASE or DECODE statement

Question

Hi experts,
I need to write a SQL to select order_num, cntry_cde, prod_id and Qty by joining order_num on PROD_ORDER and PROD_ORDER_TXT.
Here is my sample data
PRODORDER_               
order_num     cntry_cde     Prod_id     Qty
100     US     A1     5
101     US     A2     10
102     AU     A3     4
103     AU     A4     9
104     IN     A5     3
PRODORDER_TXT_               
order_num     cntry_cde     Prod_id     
100     US     A1     
101     US     A2     
102     NZ     A3     
103     AU     A4     
104          A5     
Here is the requirement,
1) If the cntry_cde in PROD_ORDER is same as cntry_cde in PROD_ORDER_TXT then select PROD_ORDER.cntry_cde (orders 100, 101, 103)
2) If they are different, pick the country code from PROD_ORDER_TXT (order 102, AU <> NZ)
3) If they are different and PROD_ORDER_TXT.cntry_cde is NULL, I cannot use it as cntry_cde in my report (order 104). It happenend just because of the bad data at source.
I cannot avoid it. Then simply use the cntry_cde from PROD_ORDER
Output expected
100     US     A1     5
101     US     A2     10
102     NZ     A3     4 -- AU changed to NZ
103     AU     A4     9
104     IN     A5     3 -- IN retained as PROD_ORDER_TXT.cntry_cde is null
sample table creation and insert statements are below
create table prod_order
(order_num number,
cntry_cde CHAR(2),
prod_id VARCHAR2(6),
qty number)
create table prod_order_txt
(order_num number,
cntry_cde CHAR(2),
prod_id VARCHAR2(6))
insert into prod_order values (100, 'US', 'A1',5);
insert into prod_order values (101, 'US', 'A2',1);
insert into prod_order values (102, 'AU', 'A3',4);
insert into prod_order values (103, 'AU', 'A4',9);
insert into prod_order values (104, 'IN', 'A5',3);
insert into prod_order_txt values (100,'US','A1');
insert into prod_order_txt values (101,'US','A2');
insert into prod_order_txt values (102,'NZ','A3');
insert into prod_order_txt values (103,'AU','A4');
insert into prod_order_txt values (104,NULL,'A5');
commit;
Thanks for your help in advance
Edited by: sarvan on Mar 28, 2012 1:39 PM

Answer 1

Hello
Thank you for posting all of the ddl and test data along with your expected output - very helpful!. One small point would be to remember to type {noformat}{noformat} before and after any section of code or data in your post so that formatting is retained.  Anyway, this should be a simple join and a combination of CASE and NVL...Select
po.order_num,
CASE
WHEN po.cntry_cde != NVL(pot.cntry_cde,po.cntry_cde)
THEN
pot.cntry_cde
ELSE
po.cntry_cde
END cntry_code,
po.prod_id,
po.qty
FROM
prod_order po
JOIN
prod_order_txt pot
ON
( po.order_num = pot.order_num
ORDER_NUM CN PROD_I QTY
100 US A1 5
101 US A2 1
102 NZ A3 4
103 AU A4 9
104 IN A5 3
5 rows selected.
HTH
David
Edited by: Bravid on Mar 28, 2012 8:32 AM
corrected !=