INNER JOIN

INNER JOIN combines rows from two tables by finding records that match on both sides, silently leaving out anything that has no partner.

About 5–10 minutes · no sign-up needed

Example

Matching Retail Orders to Customers with INNER JOIN

SELECT o.order_id, o.revenue, c.region, c.channel
FROM orders o
INNER JOIN customers c
  ON o.customer_id = c.customer_id

Result:

order_id	revenue	region	channel
O2001	129.99	Northeast	Online
O2002	54.5	Southeast	Mobile
O2003	310.0	West	Online
O2004	89.75	Midwest	In-Store

After SELECT, list the column names you want, separated by commas.
```
SELECT o.order_id, o.revenue, c.region, c.channel
```

FROM tells SQL which table to pull the data from.

SELECT o.order_id, o.revenue, c.region, c.channel
FROM orders o

INNER JOIN returns rows that match in both tables.

SELECT o.order_id, o.revenue, c.region, c.channel
FROM orders o
INNER JOIN customers c
  ON o.customer_id = c.customer_id;

Try each one in your head first, then open the answer.

1. Write a query that combines orders and customers on the customer_id column, returning only matching rows.

SELECT * FROM orders INNER JOIN customers ON orders.customer_id = customers.customer_id

2. Join orders and returns on order_id to see which orders have been returned, keeping only matching rows.

SELECT * FROM orders INNER JOIN returns ON orders.order_id = returns.order_id

3. Look at the products and reviews tables above. Find the column they share and write a query that joins them on it, returning only matching rows.

SELECT * FROM products INNER JOIN reviews ON products.product_id = reviews.product_id

4. Examine the orders and shipments tables. Identify the column they have in common and write an INNER JOIN using that column.

SELECT * FROM orders INNER JOIN shipments ON orders.order_id = shipments.order_id

5. Look at the suppliers and supplier_products tables. Find the column they share and use it to write an INNER JOIN between them.

SELECT * FROM suppliers INNER JOIN supplier_products ON suppliers.supplier_id = supplier_products.supplier_id

Learn it by doing. This lesson is a short hands-on level on Bampaa: see it work, then build and write it yourself, with instant feedback.

About 5–10 minutes · no sign-up needed