How to join results from two tables in Oracle 10 - sql

Question

Let say that I have 2 tables with the same structure : STOCK and NEW_STOCK.
These tables have a primary key composed of (ID_DATE, ID_SELLER, ID_INVOICE, ID_DOC).
Now, I need to get for every (ID_DATE, ID_SELLER, ID_INVOICE, ID_DOC), the value of the amount (field AMOUNT) regarding this requirement:
If a record is present in NEW_STOCK, I get the AMOUNT from NEW_STOCK, otherwise, I get the AMOUNT from STOCK table.
Note that ID_DATE and ID_SELLER are the inputs given to the query, i.e. a query that considers only STOCK table will look like :
select AMOUNT, ID_DATE, ID_SELLER, ID_INVOICE
from STOCK
where ID_DATE = 1
and ID_SELLER = 'SELL1';
STOCK :
+---------+-----------+------------+--------+--------+
| ID_DATE | ID_SELLER | ID_INVOICE | ID_DOC | AMOUNT |
+---------+-----------+------------+--------+--------+
| 1 | SELL1 | IN1 | DOC1 | 100 |
| 1 | SELL1 | IN2 | DOC2 | 50 |
| 1 | SELL1 | IN3 | DOC3 | 42 |
+---------+-----------+------------+--------+--------+
NEW_STOCK:
+---------+-----------+------------+--------+--------+
| ID_DATE | ID_SELLER | ID_INVOICE | ID_DOC | AMOUNT |
+---------+-----------+------------+--------+--------+
| 1 | SELL1 | IN2 | DOC2 | 12 |
+---------+-----------+------------+--------+--------+
Then, I must get the following results:
+---------+-----------+------------+--------+--------+
| ID_DATE | ID_SELLER | ID_INVOICE | ID_DOC | AMOUNT |
+---------+-----------+------------+--------+--------+
| 1 | SELL1 | IN1 | DOC1 | 100 |
| 1 | SELL2 | IN2 | DOC2 | 12 |
| 1 | SELL3 | IN3 | DOC3 | 42 |
+---------+-----------+------------+--------+--------+
ps: I'm working on Oracle 10.

Answer 1

Use outer join and NVL(arg1, arg2) function.
It returns first argument if it is not NULL, otherwise it returns second argument. Example:
select s.AMOUNT, s.ID_DATE, s.ID_SELLER, s.ID_INVOICE,
NVL(n.AMOUNT, s.AMOUNT) amount
from STOCK s, NEW_STOCK n
where s.ID_DATE = n.ID_DATE(+)
and s.ID_SELLER = n.ID_SELLER(+)
and s.ID_INVOICE = n.ID_INVOICE(+)
and s.ID_DOC = n.ID_DOC(+)
and s.ID_DATE = 1
and s.ID_SELLER = 'SELL1';
You can use LEFT OUTER JOIN syntax instead of (+) if you find it more readable. I'm using Oracle since v7 and I like (+) more.
Here is LEFT OUTER JOIN syntax:
select s.AMOUNT, s.ID_DATE, s.ID_SELLER, s.ID_INVOICE,
NVL(n.AMOUNT, s.AMOUNT) amount
from STOCK s left outer join NEW_STOCK n
on s.ID_DATE = n.ID_DATE
and s.ID_SELLER = n.ID_SELLER
and s.ID_INVOICE = n.ID_INVOICE
and s.ID_DOC = n.ID_DOC
where s.ID_DATE = 1
and s.ID_SELLER = 'SELL1';

Answer 2

SELECT * FROM (
SELECT * FROM new_stock
UNION ALL
SELECT * FROM stock
WHERE (ID_DATE,ID_SELLER,ID_INVOICE,ID_DOC) NOT IN
(SELECT ID_DATE,ID_SELLER,ID_INVOICE,ID_DOC FROM new_stock)
)
WHERE ID_DATE = 1
AND ID_SELLER = 'SELL1';

Answer 3

The following should work for it:
SELECT s.AMOUNT, s.ID_DATE, s.ID_SELLER, s.ID_INVOICE
FROM STOCK s
LEFT JOIN NEW_STOCK ns
ON s.ID_DATE = ns.ID_DATE
AND s.ID_SELLER = ns.ID_SELLER
AND s.ID_INVOICE = ns.ID_INVOICE
WHERE s.ID_DATE = 1
AND s.ID_SELLER = 'SELL1'
AND ns.ID_DATE IS NULL
UNION
SELECT AMOUNT, ID_DATE, ID_SELLER, ID_INVOICE
FROM NEW_STOCK
WHERE ID_DATE = 1
AND ID_SELLER = 'SELL1';
Exclude the matched rows from a LEFT JOIN and UNION that set with the results from the NEW_STOCK table.

Answer 4

SELECT COALESCE(NS.AMOUNT, S.AMOUNT) AMOUNT,
S.ID_DATE,
S.ID_SELLER,
S.ID_INVOICE
FROM STOCK S
LEFT JOIN NEW_STOCK NS ON S.ID_DATE = NS.ID_DATE
AND S.ID_SELLER = NS.ID_SELLER
AND S.ID_INVOICE = NS.ID_INVOICE
AND S.ID_DOC = NS.ID_DOC
WHERE S.ID_DATE = 1
AND S.ID_SELLER = 'SELL1'