SQL Inner Join

SQL INNER JOIN

The INNER JOIN returns only rows that have matching values in both tables.

Tip: You can use just JOIN instead of INNER JOIN, as INNER is the default join type.

INNER JOIN Syntax

<p><code class="sqlHigh">
SELECT <em>column_name(s)</em><br/>
FROM <em>table1</em><br/>
INNER JOIN <em>table2<br/> </em>ON <em>table1.column_name </em>=<em> table2.column_name</em>;
</code></p>

Note: The syntax combines two tables based on a related column, and the ON keyword is used to specify the matching condition.

INNER JOIN Example

Look at a product in the Products table:

And look at a row in the Categories table:

Here we see that the related column between the two tables above, is the "CategoryID" column.

Now we create an INNER JOIN on the "Products" table and the "Categories" table, via the CategoryID field:

Example

  SELECT ProductID, ProductName, CategoryName
FROM Products
INNER JOIN
  Categories ON Products.CategoryID = Categories.CategoryID;

Note: INNER JOIN returns only rows with a match in both tables. This means that if there is a product with no CategoryID, or with a CategoryID not present in the Categories table, that row will not be returned in the result.

Naming the Columns

It is a good practice to also include the table name when specifying columns in SQL joins:

Example

SELECT Products.ProductID, Products.ProductName, Categories.CategoryName

FROM Products

INNER JOIN Categories ON Products.CategoryID = Categories.CategoryID;

The example above works without specifying table names, because none of the specified column names are present in both tables. However, if you add the CategoryID column in the SELECT statement, an error occurs, if you do not specify the table name. This is because the CategoryID column is present in both tables.

JOIN or INNER JOIN

JOIN and INNER JOIN will return the same result.

INNER is the default join type for JOIN, so when you write JOIN the parser actually writes INNER JOIN.

Example

SELECT Products.ProductID, Products.ProductName, Categories.CategoryName

FROM Products

JOIN Categories ON Products.CategoryID = Categories.CategoryID;

JOIN Multiple Tables

You can join more than two tables by adding multiple INNER JOIN clauses in your query.

The following SQL selects all orders with customer and shipper information:

Example

  SELECT Orders.OrderID, Customers.CustomerName, Shippers.ShipperName
FROM
  Orders
INNER JOIN Customers ON Orders.CustomerID = Customers.CustomerID

  INNER JOIN Shippers ON Orders.ShipperID = Shippers.ShipperID;

Here is the Shippers table: