LEFT vs RIGHT
- SQL course
- Intermediate
- Lesson 11/115
- 4 min
Choose the right outer join for the task.
LEFT vs RIGHT
LEFT and RIGHT JOIN apply the same logic from opposite directions. Swapping table order converts one into the other.
SELECT c.name, o.id
FROM customers c
LEFT JOIN orders o ON o.customer_id = c.id;You can get the same result with RIGHT JOIN too.
c.name, o.id is selected from customers c. orders o is joined on o.customer_id = c.id, keeping every row of the left table.
LEFT vs RIGHT — details
Most developers prefer LEFT JOIN because reading left-to-right feels natural. RIGHT JOIN is rarely used.
Mixing LEFT and RIGHT JOIN in one query makes it hard to read; putting the main table first and always using LEFT JOIN is a good habit.
Practice LEFT vs RIGHT
Keep customers on the left and LEFT JOIN with orders.
Starter code
-- pick direction
SELECT c.name, o.id
FROM customers cSample solution
SELECT c.name, o.id
FROM customers c
LEFT JOIN orders o ON o.customer_id = c.id;Expected output
name id Ayşe 1 Fatma NULL
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Pick the direction
SELECT c.name, o.id
FROM customers c
____ orders o ON o.customer_id = c.id;SELECT c.name, o.id
FROM customers c
LEFT JOIN orders o ON o.customer_id = c.id;Explanation: LEFT JOIN is the right answer.
2 LEFT vs RIGHT: match the terms
| Term | Meaning |
|---|---|
LEFT JOIN |
all left |
RIGHT JOIN |
all right |
NULL |
empty |
ON |
condition |
3 Which direction is preferred over RIGHT JOIN?
- INNER JOIN
- LEFT JOIN Correct answer
- CROSS JOIN
- UNION
Explanation: LEFT JOIN is preferred as it reads more naturally.