Hello Reader, A common analytics question that sounds simple but isn't: "Which customers have booked the same type of expedition more than once?" You can't answer this with a regular JOIN between two different tables. The information lives in one table. You need to compare rows within that table to find patterns. That's what a self-JOIN does. It joins a table to itself. It sounds unusual, but once you see the pattern, you'll recognize situations where it's exactly what you need. The Business...
11 days ago • 4 min read
Hello Reader, You've built a clean customer report. Locations, booking history, revenue by region. You send it off to whoever asked for it. Ten minutes later: "Why does this report show blank cells in the location column? And why do the totals not add up?" Welcome to the NULL problem. You're going to learn how to solve it once and for all today. In the Summit Adventures database (the fake adventure tourism company I created to help people learn business analytics), 78.2% of customers don't...
18 days ago • 4 min read
Hello Reader, Imagine you're an analyst at Summit Adventures. Monday morning, you get called into a meeting and your VP asks: "How's revenue looking across our expedition types?" You pull up your analysis. You've got clean numbers. You present them: "Cultural expeditions brought in $374K. Photography brought in $370K. Hiking was $352K. Safari was $349K. Climbing was $298K." Silence. Then someone asks: "Okay... but what should we do about it?" You've answered the question accurately. But you...
25 days ago • 5 min read
Hi Reader, Time-based questions come up constantly in business. "Show me bookings from the last 90 days." "How does this quarter compare to last quarter?" "What's the week-over-week trend?" And most analysts handle them the worst possible way: by hardcoding dates. -- Don't do this WHERE booking_date >= '2026-01-01' AND booking_date < '2026-04-01' This works today. Next quarter, you have to remember to change the dates. You won't remember. And the report will silently show stale data until...
about 1 month ago • 4 min read
Hey Reader, Most analysts can't answer something like this: "Which of our guides are generating the most revenue, and are we assigning them to the right expeditions?" This isn't a one-step question. You need to: Calculate revenue per guide Look at which expedition types they're assigned to Compare guide revenue to expedition category performance Identify mismatches (top guides on underperforming products, or vice versa) That's four analytical steps. Trying to write this as a single SQL query...
about 1 month ago • 4 min read
Hey Reader, Quick question: Could a colleague open your most recent SQL query and understand what it does without asking you a single question? If the answer is "probably not," this newsletter is for you. Writing SQL that works is step one. Writing SQL that someone else can read, trust, and maintain — that's the skill that changes how people see your work. Why This Matters More Than You Think Here's what I've noticed over 15+ years in analytics: the analysts who get promoted aren't always the...
about 2 months ago • 4 min read
Hey Reader, Imagine you're presenting a finding to your team: "Customer A spent $4,200 with us." The first question from the room: "Is that a lot?" Most analysts learning SQL don't realize that, without context, the number means nothing. You need comparison. Is the average customer spend $500 or $5,000? Is $4,200 in the top 10% or the middle of the pack? This is the "compared to what?" problem, and subqueries solve it elegantly. Numbers without context don't drive decisions. Executives don't...
about 2 months ago • 4 min read
Hello Reader, Almost every business question boils down to one of two things: "How many?" (COUNT) "How much?" (SUM) How many customers booked this month? How much revenue did we generate? How many trips were cancelled? How much did we lose? Once you're comfortable with COUNT and SUM, you can answer the majority of questions that come your way (like sales analytics using SQL). Let me show you both patterns using a real business scenario. The Scenario Your operations manager asks: "Give me a...
2 months ago • 4 min read
HeyReader, Most analysts never think to ask: "Why are our customers cancelling?" Everyone looks at bookings. Everyone reports revenue. But the data hiding in your cancelled orders often tells a more important story than your completed ones. And analysts that want to move from beginner to intermediate SQL skill level have an unfair advantage here. Because there's a sequence to work through this kind of problem. That's what we're covering here. At Summit Adventures (the fake adventure tourism...
2 months ago • 4 min read