Summary - LEFT and RIGHT JOIN
- SQL course
- Intermediate
- Lesson 12/115
- 5 min
Write a missing-record report with LEFT JOIN.
Summary - LEFT and RIGHT JOIN
LEFT JOIN keeps all rows of the left table, RIGHT JOIN keeps all rows of the right table. The unmatched side becomes NULL.
SELECT c.name, o.id
FROM customers c
LEFT JOIN orders o ON o.customer_id = c.id;Summary left join.
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.
Practice Summary - LEFT and RIGHT JOIN
Summary: LEFT JOIN customers with orders.
Starter code
-- summary left join
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 What happens to the unmatched side?
- It is deleted
- An empty string
- NULL Correct answer
- An error
Explanation: The unmatched side comes as NULL.
2 Summary - LEFT and RIGHT JOIN: match the terms
| Term | Meaning |
|---|---|
LEFT JOIN |
all left |
RIGHT JOIN |
all right |
NULL |
empty |
COALESCE |
default |