You have tables users(id, name) and logins(user_id, login_time). Write a query to find users who never logged in and order them by name.

hard📝 Application Q8 of 15

SQL - LEFT and RIGHT JOIN

You have tables users(id, name) and logins(user_id, login_time). Write a query to find users who never logged in and order them by name.

ASELECT u.name FROM users u FULL JOIN logins l ON u.id = l.user_id WHERE l.user_id IS NOT NULL ORDER BY u.name;

BSELECT u.name FROM users u INNER JOIN logins l ON u.id = l.user_id WHERE l.user_id IS NULL ORDER BY u.name;

CSELECT u.name FROM users u RIGHT JOIN logins l ON u.id = l.user_id WHERE u.id IS NULL ORDER BY u.name;

DSELECT u.name FROM users u LEFT JOIN logins l ON u.id = l.user_id WHERE l.user_id IS NULL ORDER BY u.name;

Step-by-Step Solution

Solution:

Step 1: Use LEFT JOIN to keep all users
LEFT JOIN keeps all users and matches logins or NULL if none.
Step 2: Filter users with no logins
WHERE l.user_id IS NULL selects users who never logged in.
Step 3: Order results by user name
ORDER BY u.name sorts the output alphabetically.
Final Answer:
SELECT u.name FROM users u LEFT JOIN logins l ON u.id = l.user_id WHERE l.user_id IS NULL ORDER BY u.name; -> Option D
Quick Check:
LEFT JOIN + NULL filter + ORDER BY = unmatched users sorted [OK]

Quick Trick: LEFT JOIN + NULL filter + ORDER BY finds and sorts unmatched rows [OK]

Common Mistakes:

MISTAKES

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