A JOIN clause is used to combine rows from two or more tables, based on a related column between them.
Let's look at a selection from the "Orders" table:
Then, look at a selection from the "Customers" table:
|1||Alfreds Futterkiste||Maria Anders||Germany|
|2||Ana Trujillo Emparedados y helados||Ana Trujillo||Mexico|
|3||Antonio Moreno Taquería||Antonio Moreno||Mexico|
Notice that the "CustomerID" column in the "Orders" table refers to the "CustomerID" in the "Customers" table. The relationship between the two tables above is the "CustomerID" column.
Then, we can create the following SQL statement (that contains an INNER JOIN), that selects records that have matching values in both tables:
SELECT Orders.OrderID, Customers.CustomerName, Orders.OrderDate
INNER JOIN Customers ON Orders.CustomerID=Customers.CustomerID;