SQL Joins
The SQL JOIN Clause
The JOIN clause is used to combine rows from two or more tables, based on a related column between them.
Here are the different types of JOINs in SQL:
(INNER) JOIN: Returns only rows that have matching values in both tablesLEFT (OUTER) JOIN: Returns all rows from the left table, and only the matched rows from the right tableRIGHT (OUTER) JOIN: Returns all rows from the right table, and only the matched rows from the left tableFULL (OUTER) JOIN: Returns all rows when there is a match in either the left or right table
Look at an order in "Orders" table:
| OrderID | CustomerID | OrderDate |
|---|---|---|
| 10308 | 2 | 1996-09-18 |
Then, look at a customer in the "Customers" table:
| CustomerID | CustomerName | ContactName | Country |
|---|---|---|---|
| 2 | Ana Trujillo Emparedados y helados | Ana Trujillo | Mexico |
Here we see 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:
Example
SELECT Orders.OrderID, Customers.CustomerName, Orders.OrderDate
FROM Orders
INNER JOIN Customers ON Orders.CustomerID=Customers.CustomerID;
Try it Yourself »
and it will produce something like this:
| OrderID | CustomerName | OrderDate |
|---|---|---|
| 10308 | Ana Trujillo Emparedados y helados | 1996-09-18 |
| 10365 | Antonio Moreno Taquería | 1996-11-27 |
| 10383 | Around the Horn | 1996-11-15 |
| 10355 | Around the Horn | 1996-12-16 |
| 10278 | Berglunds snabbköp | 1996-12-16 |
