Self join concept in SQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to select all employees and their managers using a self join.

SQL

SELECT e.name AS employee, m.name AS manager FROM employees e JOIN employees m ON e.manager_id = [1].id;

Drag options to blanks, or click blank then click option'

Aemployees

Bm

Ce

Dmanagers

Attempts:

3 left

💡 Hint

Common Mistakes

Using the same alias for both tables causes confusion.

Joining on the wrong columns or missing the alias before the column.

The alias m refers to the managers table (which is the same employees table but aliased). We join on e.manager_id = m.id to link employees to their managers.

2fill in blank

medium

Complete the code to find employees whose manager's name is 'Alice'.

SQL

SELECT e.name FROM employees e JOIN employees m ON e.manager_id = m.id WHERE m.name = [1];

Drag options to blanks, or click blank then click option'

A'Bob'

B'Manager'

C'Alice'

D'John'

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting quotes around the string value.

Using the employee's name instead of the manager's name in the WHERE clause.

We want to find employees whose manager's name is 'Alice'. So the condition is m.name = 'Alice'.

3fill in blank

hard

Fix the error in the code to correctly list employees and their managers.

SQL

SELECT e.name, m.name FROM employees e JOIN employees m ON e.manager_id = [1].id;

Drag options to blanks, or click blank then click option'

Am

Be

Cemployees

Dmanagers

Attempts:

3 left

💡 Hint

Common Mistakes

Joining on the wrong column causing no results or errors.

Using the employee alias instead of the manager alias in the join condition.

The join condition should match e.manager_id = m.id, not m.manager_id. So the alias before id is m.

4fill in blank

hard

Fill both blanks to select employees and their managers who work in the same department.

SQL

SELECT e.name, m.name FROM employees e JOIN employees m ON e.manager_id = m.id WHERE e.[1] = m.[2];

Drag options to blanks, or click blank then click option'

Adepartment_id

Bmanager_id

Cid

Dname

Attempts:

3 left

💡 Hint

Common Mistakes

Using manager_id or id instead of department_id for the comparison.

Comparing employee's department_id with manager's name or other unrelated columns.

To find employees and managers in the same department, compare e.department_id with m.department_id.

5fill in blank

hard

Fill all three blanks to create a query that lists employees, their managers, and the manager's department name.

SQL

SELECT e.name AS employee, m.name AS manager, d.[1] FROM employees e JOIN employees m ON e.[2] = m.[3] JOIN departments d ON m.department_id = d.id;

Drag options to blanks, or click blank then click option'

Adepartment_name

Bmanager_id

Cid

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong column names for joins causing errors.

Selecting wrong columns from the departments table.

The query selects the department name from the departments table. The join between employees and managers is on e.manager_id = m.id.