SQL for data analysts

46 levels in 8 chapters

Learn SQL the way analysts use it: real tickets from colleagues, answered with queries on a full store database, right in your browser.

By the end you can filter, join, group and rank a real company database, and write the CTEs and window functions interviewers ask about. Every level is open; the path only suggests an order.

Chapter 1 · 5 levels

SELECT basics

5 lanterns to light

  1. Look at the product catalog
  2. Pick only the columns you need
  3. Compute margin per product
  4. List the category tree
  5. Boss Boss: catalog snapshot

Chapter 2 · 6 levels

Filtering rows

6 lanterns to light

  1. Find refunded orders
  2. Gift ideas under $50
  3. Orders from March 2024
  4. Find Gmail customers
  5. The NULL comparison trap
  6. Boss Boss: data quality sweep

Chapter 3 · 5 levels

Sorting and limits

5 lanterns to light

  1. Price list, most expensive first
  2. The 10 most recent orders
  3. Page two of the price list
  4. Missing costs on top
  5. Boss Boss: homepage merchandising lists

Chapter 4 · 6 levels

Aggregates and GROUP BY

6 lanterns to light

  1. How many customers came from referrals?
  2. Total units and revenue
  3. Orders by channel and status
  4. Our most loyal customers
  5. Why does this query fail?
  6. Boss Boss: performance snapshot

Chapter 5 · 6 levels

JOINs

6 lanterns to light

  1. Revenue by category
  2. Customers who never ordered
  3. App orders per business customer
  4. Lines per order without double counting
  5. Who reports to whom
  6. Boss Boss: category scorecard

Chapter 6 · 6 levels

CASE, dates and strings

6 lanterns to light

  1. Products by price band
  2. Cancellation rate by channel
  3. Monthly revenue for 2025
  4. How long until items come back?
  5. Customers by state, cleaned up
  6. Boss Boss: customer base profile

Chapter 7 · 6 levels

Subqueries and CTEs

6 lanterns to light

  1. Products priced above average
  2. Customers who returned something
  3. Customer lifetime value
  4. Shipping and merchandise revenue per channel
  5. Find duplicate customer records
  6. Boss Boss: first orders and repeat purchases

Chapter 8 · 6 levels

Window functions

6 lanterns to light

  1. Top 3 products in every category
  2. ROW_NUMBER vs RANK vs DENSE_RANK
  3. Year-to-date revenue
  4. Month-over-month growth
  5. 7-day moving average of orders
  6. Boss Boss: cohort retention

Jessica Turner · Merchandising Manager

"Welcome aboard! Before we get into anything fancy, could you pull up the whole product catalog so you can see what we sell?"

Light the next lantern