SQL > SQL JOIN > 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  Txn_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 result set. 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:

STORE  SALES
Los Angeles  1800
San Diego  250
Boston  700

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.

Next: SQL Outer Join

This page was last updated on May 09, 2022.




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