SQL Subqueries - Practical Examples Tutorial

Write a Subquery to Find Departments with More Than 5 Employees

Write an SQL query using a subquery to list departments that have more than five employees.

Expected output: List of department names with employee count greater than 5.

Hint: Use a subquery in the WHERE clause with COUNT and GROUP BY.

Use a Subquery in SELECT to Show Employee and Their Manager's Name

Write a query that shows each employee's name and their manager's name using a subquery in the SELECT clause.

Expected output: Table with employee_name and manager_name columns.

Hint: Use a correlated subquery referencing the manager_id.

Create a Derived Table to Calculate Total Sales per Region

Write a query using a subquery in the FROM clause to calculate total sales per region.

Expected output: Table showing region names and their total sales.

Hint: Group sales by region inside the subquery and join with region details.

A correlated subquery is a subquery that references columns from the outer query and executes once for each row processed by the outer query.

You use a subquery in the FROM clause to create a derived table or inline view that the outer query can join or select from, useful for breaking down complex queries.

A subquery is a nested query that returns data for the outer query, while a JOIN combines rows from two or more tables based on related columns. JOINs are often more efficient.