Summary - EXISTS
- SQL course
- Intermediate
- Lesson 58/115
- 5 min
Find customers with no orders using NOT EXISTS.
Summary - EXISTS
EXISTS checks whether a subquery returns rows. NOT EXISTS finds missing records.
SELECT name FROM customers c
WHERE NOT EXISTS (SELECT 1 FROM orders o WHERE o.customer_id = c.id);Summary EXISTS query.
name is selected from customers c. WHERE keeps only the rows where NOT EXISTS (SELECT 1 FROM orders o WHERE o.customer_id = … holds.
Practice Summary - EXISTS
Summary: find customers without orders using NOT EXISTS.
Starter code
-- summary exists
SELECT name FROM customers c
WHERESample solution
SELECT name FROM customers c
WHERE NOT EXISTS (SELECT 1 FROM orders o WHERE o.customer_id = c.id);Expected output
name Fatma Ali
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 What finds customers without orders?
- NOT EXISTS Correct answer
- EXISTS
- COUNT
- SUM
Explanation: NOT EXISTS finds missing records.
2 Summary - EXISTS: match the terms
| Term | Meaning |
|---|---|
EXISTS |
existence |
NOT EXISTS |
missing |
fast |
short-circuit |
NULL |
unaffected |