Sqlism

Loading…

Sqlism

Tools Blog Challenge Interview On the Job Quiz Resources Pricing

Sign in Sign in to unlock

Progress synced across every device
Quiz & challenge history saved
Star your favorite SQL tools
Favorite articles to read later
Interview prep tracked by topic

HR & People · Ticket #1

Headcount and average salary by department

Junior Free 8 min LEFT JOINAVG / ROUNDON vs WHERE

people-analytics PeopleFirst SQ RI

PeopleFirst database

What you'll learn

LEFT JOIN from the table whose rows must all appear
Put right-table filters in ON to keep empty groups
COUNT(column) ignores NULLs, COUNT(*) doesn't

More tickets

Next · Ticket #2 Who earns more than their manager? All tickets

Learn

SQL Playground Challenges Daily Challenge SQL on the Job Skill Check Certification Quizzes Interview Prep Resources Blog

Company

About Contact Pricing Report a Bug

Legal

Terms Privacy Disclaimer Refund Policy Cancellation Policy

Featured Posts

Blog · Analytics & Reporting Top N Per Category in SQL (Top 3 Per Group) ROW_NUMBER with PARTITION BY, wrapped in a CTE — the classic greatest-n-per-group pattern… Blog · Interview Amazon Business Analyst SQL Interview Questions Marketplace-style schema, metrics-driven questions — top categories, late deliveries, seller…

Unlock Sqlism Pro today

Pay once, keep it forever — advanced tools, full interview prep, and every downloadable resource.

© 2026 Sqlism. All rights reserved.

We Use Cookies (But Not the Chocolate Chip Kind) 🍪

We use essential cookies to make SQLism work (like remembering your theme preference). Optional cookies help us understand how you use our site to make it better. By clicking "Accept All", you agree to our use of cookies. Learn more or customize your preferences.

Cookie Preferences

Hey there, SQL explorer! 👋

We believe in transparency. Here you can choose which cookies you're comfortable with. Essential cookies are required for the site to function (like keeping you logged in and remembering your theme).

Essential Cookies

Required for the site to work. Cannot be turned off. Includes theme preferences and session management.

Analytics Cookies

Help us understand how you use SQLism (most popular queries, time spent) so we can improve your learning experience.

Personalization Cookies

Remember your progress, preferred difficulty level, and suggest relevant SQL challenges.