Joins & Aggregations

Preview — 3 of 10 questions

What does an INNER JOIN return?

javascript

SELECT u.name, o.total
FROM users u
INNER JOIN orders o ON u.id = o.user_id;

AOnly rows where there is a match in both tables

BAll rows from orders, with NULL for non-matching users

CAll rows from users, with NULL for non-matching orders

DAll rows from both tables, with NULLs for non-matches on either side

Which query finds all users, including those who have never placed an order?

javascript

-- Table users(id, name) — Table orders(id, user_id, total)

ASELECT u.name, o.total FROM users u INNER JOIN orders o ON u.id = o.user_id

BSELECT u.name, o.total FROM users u LEFT JOIN orders o ON u.id = o.user_id

CSELECT u.name, o.total FROM orders o RIGHT JOIN users u ON u.id = o.user_id

DBoth B and C are correct

Which query returns the total revenue per customer?

javascript

-- Table: orders(id, user_id, total)

ASELECT user_id, SUM(total) FROM orders

BSELECT user_id, SUM(total) FROM orders GROUP BY user_id

CSELECT user_id, TOTAL(total) FROM orders GROUP BY user_id

DSELECT user_id, SUM(total) FROM orders AGGREGATE BY user_id

Answer all 10 questions (7 more), see explanations for every answer, and track your score.