Subqueries
Learn how to nest queries within queries.
Learn how to nest queries within queries. This hands-on tutorial focuses on practical implementation of subqueries concepts.
What is a Subquery?
A subquery is a query nested inside another query. It can be used in SELECT, FROM, WHERE, and other clauses.
Subqueries are executed first, and their result is passed to the outer query.
Single-Row Subquery
A single-row subquery returns one row with one column. It is often used with comparison operators (=, >, <).
Example: Products More Expensive than Average
Find all products that have a price higher than the average price.
Multi-Row Subquery
A multi-row subquery returns multiple rows. It is often used with the IN operator.
Example: Customers who have ordered "Chais"
Note: Since our simplified playground data doesn't fully link Orders effectively without more setup, let's use a conceptual example or a different data set.
For now, let's find Customers from countries where we also have suppliers (assuming we had a suppliers table). Since we don't, let's try finding customers who are in the same country as 'Alfreds Futterkiste'.