The SQL JOIN
joins two tables based on a common column, and selects records that have matching values in these columns.
Example
SELECT Customers.customer_id, Customers.first_name, Orders.amount
FROM Customers
JOIN Orders
ON Customers.customer_id = Orders.customer;
Here's how this code works:

Here, the SQL command selects customer_id and first_name columns (from the Customers table) and the amount column (from the Orders table).
And, the result set will contain those rows where there is a match between customer_id (of the Customers table) and customer (of the Orders table).
Types of SQL JOINs
The JOIN
command we performed earlier is INNER JOIN
. There are mainly four types of joins.
- INNER JOIN (Same as
JOIN
) - LEFT JOIN
- RIGHT JOIN
- FULL OUTER JOIN
SQL JOIN and Aliases
We can use AS aliases with table names to make our snippet short and clean. For example,
SELECT C.customer_id, C.first_name, O.amount
FROM Customers AS C
JOIN Orders AS O
ON C.customer_id = O.customer;
Also, we can change the column names temporarily using AS aliases. For example,
SELECT C.customer_id AS cid, C.first_name AS name, O.amount
FROM Customers AS C
JOIN Orders AS O
ON C.customer_id = O.customer;
Here, these snippets would work exactly the same as earlier.