SQL Inner Join

An inner join in SQL returns rows where there is at least one match on both tables. Let's assume that we have the following two tables,

Table Store_Information

store_name	Sales	Date
Los Angeles	$1500	Jan-05-1999
San Diego	$250	Jan-07-1999
Los Angeles	$300	Jan-08-1999
Boston	$700	Jan-08-1999

Table Geography

region_name	store_name
East	Boston
East	New York
West	Los Angeles
West	San Diego

We want to find out sales by store, and we only want to see stores with sales listed in the report. To do this, we can use the following SQL statement using INNER JOIN:

SELECT A1.store_name STORE, SUM(A2.Sales) SALES
FROM Geography A1
INNER JOIN Store_Information A2
ON A1.store_name = A2.store_name
GROUP BY A1.store_name

Result:

By using INNER JOIN, the result shows 3 stores, even though we are selecting from the Geography table, which has 4 rows. The row "New York" is not selected because it is not present in the Store_Information table.