INNER JOIN

INNER JOIN is the most common join.

It returns rows where the join condition matches in both tables.

Core Concepts

flowchart TD
  A[Left table row] --> B{Match in right table?}
  B -->|Yes| C[Return combined row]
  B -->|No| D[Exclude row]

Piece	Example
Left table	customers_join c
Right table	orders_join o
Predicate	c.customer_id = o.customer_id

Code Examples

-- Return only customers who have orders.
SELECT
  c.customer_id,
  c.name,
  o.order_id,
  o.total
FROM customers_join AS c
INNER JOIN orders_join AS o
  ON c.customer_id = o.customer_id
ORDER BY c.customer_id, o.order_id;

customer_id	name	order_id	total
1	Ada	101	49.99
1	Ada	102	19.50
2	Alan	103	75.00

-- Aggregate after inner join: order count per matched customer.
SELECT c.name, count(*) AS order_count
FROM customers_join AS c
INNER JOIN orders_join AS o
  ON c.customer_id = o.customer_id
GROUP BY c.customer_id, c.name
ORDER BY c.customer_id;

name	order_count
Ada	2
Alan	1

SQLite-Specific Nuances

SQLite Nuance

In SQLite, writing JOIN without a qualifier means INNER JOIN.

Common Pitfalls / Best Practices

Pitfall

Using INNER JOIN when you actually need rows with no matches (for example, customers with zero orders).

Best Practice

Choose join type based on business question first, then write SQL.

Quick Challenge

Return only name and total for matched customer-order rows.

View Solution

SELECT c.name, o.total
FROM customers_join AS c
INNER JOIN orders_join AS o
  ON c.customer_id = o.customer_id
ORDER BY c.name, o.total;

name	total
Ada	19.50
Ada	49.99
Alan	75.00