Natural Join — SQL Technical Interview Questions & Answers

Natural Join

Natural Join

  • NATURAL JOIN matches columns that have the same name on both tables and you do not write ON. If both have roll, it joins on roll. If they also both have created_at, it joins on that too — surprise.
  • Don’t use NATURAL JOIN in production. Name the columns: JOIN … ON s.roll = m.roll. Interviews: know it, then say you avoid it.
  • Trap: NATURAL JOIN as the default in answers. Hidden extra same-name columns.
  • On the example next to this theory: Natural Join — jOIN combines rows using a match condition between tables.

Technical Interview Tip: Know NATURAL JOIN. Prefer JOIN … ON s.roll = m.roll.

Code Examples for Natural Join

Natural Join — sample query

CREATE TABLE customers (id INTEGER PRIMARY KEY, name TEXT);
CREATE TABLE orders (id INTEGER PRIMARY KEY, customer_id INTEGER, total INTEGER);
INSERT INTO customers VALUES (1, 'Asha'), (2, 'Ravi');
INSERT INTO orders VALUES (10, 1, 500), (11, 1, 200);
SELECT c.name, o.total
FROM customers c
JOIN orders o ON o.customer_id = c.id;

Natural Join — jOIN combines rows using a match condition between tables.

How to Explain Natural Join to an Interviewer

Why avoid NATURAL JOIN?

Hidden same-name columns ON is clearer