Self JOIN in MySQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to select employee names and their managers' names using a self join.

MySQL

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'

Am

Be

Cemployees

Dmanagers

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong alias like 'e.id' instead of 'm.id'.

Using the table name instead of alias in the ON clause.

The alias m refers to the managers table instance in the self join. We join on e.manager_id = m.id to link employees to their managers.

2fill in blank

medium

Complete the code to find employees who have the same manager.

MySQL

SELECT e1.name, e2.name FROM employees e1 JOIN employees e2 ON e1.[1] = e2.manager_id WHERE e1.id != e2.id;

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

Amanager_id

Bdepartment_id

Cname

Did

Attempts:

3 left

💡 Hint

Common Mistakes

Joining on employee IDs instead of manager IDs.

Using the same alias on both sides of the join condition.

We join on e1.manager_id = e2.manager_id to find employees sharing the same manager.

3fill in blank

hard

Fix the error in the self join query to correctly list employees and their managers.

MySQL

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

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

Ae.id

Bm.manager_id

Cm.id

De.manager_id

Attempts:

3 left

💡 Hint

Common Mistakes

Using employee's own ID instead of manager's ID in the join.

Confusing the aliases in the ON clause.

The join condition should be e.manager_id = m.id to link employees to their managers correctly.

4fill in blank

hard

Fill both blanks to select employees and their managers' names, including employees without managers.

MySQL

SELECT e.name AS employee, [1].name AS manager FROM employees e LEFT JOIN employees [2] ON e.manager_id = [2].id;

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

Am

Be

Dmanagers

Attempts:

3 left

💡 Hint

Common Mistakes

Using different aliases in SELECT and JOIN.

Using INNER JOIN instead of LEFT JOIN, missing employees without managers.

The alias m is used for the managers table instance. We use LEFT JOIN to include employees without managers.

5fill in blank

hard

Fill all three blanks to find employees who are also managers of others.

MySQL

SELECT DISTINCT [1].name FROM employees [2] JOIN employees [3] ON [2].id = [3].manager_id;

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

Am

Be

Dmanagers

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up aliases for employees and managers.

Not using DISTINCT, causing duplicate manager names.

Alias m is used for managers and e for employees. We join on m.id = e.manager_id to find managers who have employees.