Natural join and its risks in SQL - Mini Project: Build & Apply

Understanding Natural Join and Its Risks in SQL

📖 Scenario: You are working with two tables in a company database: employees and departments. Both tables have a column named department_id. You want to combine these tables to see employee names along with their department names.However, you need to understand how using a natural join works and what risks it might have when joining tables.

🎯 Goal: Build a SQL query using NATURAL JOIN to combine the employees and departments tables on their common column. Then, learn to identify potential risks of using natural joins.

📋 What You'll Learn

Create two tables: employees and departments with specified columns

Insert sample data into both tables

Write a SQL query using NATURAL JOIN to combine the tables

Explain the risk of using NATURAL JOIN when tables have multiple columns with the same name

💡 Why This Matters

🌍 Real World

Natural joins can simplify queries when tables share exactly one common column, but in real databases, tables often share multiple column names, so understanding risks helps avoid bugs.

💼 Career

Database developers and analysts must write correct join queries to combine data accurately. Knowing when to use or avoid NATURAL JOIN is important for data integrity.

1

Create the employees and departments tables

Write SQL statements to create a table called employees with columns employee_id (integer), employee_name (text), and department_id (integer). Also create a table called departments with columns department_id (integer) and department_name (text).

SQL

-- Create employees and departments tables
-- Your code here

Need a hint?

Use CREATE TABLE statements with the exact column names and types.

2

Insert sample data into both tables

Insert these rows into employees: (1, 'Alice', 10), (2, 'Bob', 20), (3, 'Charlie', 10). Insert these rows into departments: (10, 'HR'), (20, 'Engineering').

SQL

CREATE TABLE employees (
    employee_id INTEGER,
    employee_name TEXT,
    department_id INTEGER
);

CREATE TABLE departments (
    department_id INTEGER,
    department_name TEXT
);

-- Insert data into employees and departments
-- Your code here

Need a hint?

Use INSERT INTO statements with the exact values given.

3

Write a SQL query using NATURAL JOIN

Write a SQL query to select employee_name and department_name by joining employees and departments using NATURAL JOIN.

SQL

CREATE TABLE employees (
    employee_id INTEGER,
    employee_name TEXT,
    department_id INTEGER
);

CREATE TABLE departments (
    department_id INTEGER,
    department_name TEXT
);

INSERT INTO employees VALUES (1, 'Alice', 10);
INSERT INTO employees VALUES (2, 'Bob', 20);
INSERT INTO employees VALUES (3, 'Charlie', 10);

INSERT INTO departments VALUES (10, 'HR');
INSERT INTO departments VALUES (20, 'Engineering');

-- Write a query using NATURAL JOIN to select employee_name and department_name
-- Your code here

Need a hint?

Use SELECT employee_name, department_name FROM employees NATURAL JOIN departments;

4

Explain the risk of using NATURAL JOIN

Add a SQL comment explaining that NATURAL JOIN can be risky because it automatically joins on all columns with the same name, which might cause unexpected results if tables have multiple columns with the same name.

SQL

CREATE TABLE employees (
    employee_id INTEGER,
    employee_name TEXT,
    department_id INTEGER
);

CREATE TABLE departments (
    department_id INTEGER,
    department_name TEXT
);

INSERT INTO employees VALUES (1, 'Alice', 10);
INSERT INTO employees VALUES (2, 'Bob', 20);
INSERT INTO employees VALUES (3, 'Charlie', 10);

INSERT INTO departments VALUES (10, 'HR');
INSERT INTO departments VALUES (20, 'Engineering');

SELECT employee_name, department_name FROM employees NATURAL JOIN departments;

-- Your comment here explaining the risk of NATURAL JOIN

Need a hint?

Add a comment starting with -- explaining the risk of NATURAL JOIN.