Multi-table JOIN
- SQL course
- Beginner
- Lesson 105/115
- 4 min
Join three or more tables in one query.
JOIN and WHERE
After JOIN you can filter the combined result with WHERE.
SELECT o.id, c.name
FROM orders o
JOIN customers c ON o.customer_id = c.id
WHERE c.city = 'İstanbul';This query returns only orders from customers in Istanbul.
o.id, c.name is selected from orders o. customers c is joined on o.customer_id = c.id, keeping only matching rows. WHERE keeps only the rows where c.city = 'İstanbul' holds.
JOIN and WHERE — details
WHERE comes after JOIN and filters the merged table. The JOIN condition goes in ON; the filter goes in WHERE.
Practice JOIN and WHERE
JOIN orders and customers; return only orders from Istanbul customers.
Starter code
-- filtered join
SELECT o.id, c.name
FROM orders o
JOIN customers c ON o.customer_id = c.id
WHERESample solution
SELECT o.id, c.name
FROM orders o
JOIN customers c ON o.customer_id = c.id
WHERE c.city = 'İstanbul'Expected output
id name 1 Ayşe
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Filtered join
Question
SELECT o.id, c.name
FROM orders o
JOIN customers c ON o.customer_id = c.id
____ c.city = 'İstanbul';
Answer
SELECT o.id, c.name
FROM orders o
JOIN customers c ON o.customer_id = c.id
WHERE c.city = 'İstanbul';Explanation: After the join, WHERE filters the result; only customers in Istanbul remain.
2 Multi-table JOIN: match the terms
| Term | Meaning |
|---|---|
JOIN |
join |
ON |
join condition |
WHERE |
filter |
FROM |
table |
3 Where does the post-JOIN filter go?
- GROUP BY
- ON
- FROM
- WHERE Correct answer
Explanation: The filter goes in WHERE.