NATURAL join and its risks in PostgreSQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to perform a natural join between tables employees and departments.

PostgreSQL

SELECT * FROM employees [1] departments;

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AINNER JOIN ON

BCROSS JOIN

CLEFT JOIN

DNATURAL JOIN

Attempts:

3 left

💡 Hint

Common Mistakes

Using INNER JOIN without ON clause causes syntax error.

Using CROSS JOIN returns Cartesian product, not matching rows.

The NATURAL JOIN keyword joins two tables based on all columns with the same names in both tables.

2fill in blank

medium

Complete the code to select employee names and their department names using NATURAL JOIN.

PostgreSQL

SELECT employees.name, departments.name FROM employees [1] departments;

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ANATURAL JOIN

BJOIN ON employees.dept_id = departments.id

CLEFT JOIN ON employees.dept_id = departments.id

DCROSS JOIN

Attempts:

3 left

💡 Hint

Common Mistakes

Using JOIN ON without specifying the join condition.

Using CROSS JOIN which returns all combinations.

NATURAL JOIN automatically joins on columns with the same name, so no ON clause is needed.

3fill in blank

hard

Fix the error in the query that uses NATURAL JOIN but returns unexpected results due to extra matching columns.

PostgreSQL

SELECT * FROM orders [1] customers ON orders.customer_id = customers.id;

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ANATURAL JOIN

BINNER JOIN

CLEFT JOIN

DCROSS JOIN

Attempts:

3 left

💡 Hint

Common Mistakes

Using NATURAL JOIN when tables have multiple columns with the same name but different meanings.

Using CROSS JOIN which returns all rows combined.

Using INNER JOIN ON with explicit join condition avoids unexpected matches caused by NATURAL JOIN on multiple columns.

4fill in blank

hard

Fill both blanks to create a query that avoids NATURAL JOIN risks by specifying join columns explicitly.

PostgreSQL

SELECT * FROM sales [1] customers [2] sales.customer_id = customers.id;

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AINNER JOIN

BLEFT JOIN

CON

DUSING

Attempts:

3 left

💡 Hint

Common Mistakes

Using NATURAL JOIN which can join on unintended columns.

Using USING keyword without matching column names.

Using INNER JOIN with ON clause explicitly defines the join condition, avoiding risks of NATURAL JOIN.

5fill in blank

hard

Fill all three blanks to write a safe join query selecting employee and department names, avoiding NATURAL JOIN risks.

PostgreSQL

SELECT e.name AS employee_name, d.name AS department_name FROM employees e [1] departments d [2] e.dept_id [3] d.id;

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

AINNER JOIN

B=

CON

DLEFT JOIN

Attempts:

3 left

💡 Hint

Common Mistakes

Using NATURAL JOIN which may join on unintended columns.

Using INNER JOIN when you want to keep all employees regardless of department.

Using LEFT JOIN with ON clause and explicit equality condition safely joins tables without NATURAL JOIN risks.