SQL inner JOIN & outer JOIN 內部連接與外部連接

outer join: 想要列出一個表格中每一筆的資料， 無論它的值在另一個表格中有沒有出現



* inner JOIN (left join)
SELECT A1.region_name REGION, SUM(A2.Sales) SALES
FROM Geography A1, Store_Information A2
WHERE A1.store_name = A2.store_name
GROUP BY A1.region_name

REGION	SALES
East	$700
West	$2050

* outer JOIN (right join)
SELECT A1.store_name, SUM(A2.Sales) SALES
FROM Georgraphy A1, Store_Information A2
WHERE A1.store_name = A2.store_name (+)
GROUP BY A1.store_name

store_name	SALES
Boston	$700
New York
Los Angeles	$1800
San Diego	$250