Blog
Professor Owl's Notes
Short explanations, with examples you can copy, about SQL, Excel and working with data.
🎤Career · November 3, 2026 · 6 min
How to prepare for a SQL interview
What they ask, how to think out loud and the five topics that can't be missing.
SQL · November 2, 2026 · 7 min
Window functions without fear
ROW_NUMBER, RANK and SUM OVER explained with a track race.
🧮Excel · October 27, 2026 · 5 min
Pivot tables in 5 minutes
Group, sum and count hundreds of rows without writing a formula. The essentials to start today.
🔍Excel · October 20, 2026 · 6 min
VLOOKUP, XLOOKUP or INDEX+MATCH: which one should I use?
Three ways to look up a value in Excel. When each one works and which will save you headaches.
🧺SQL · October 13, 2026 · 5 min
WHERE or HAVING: the difference in one example
Both filter, but at different moments. A store example is enough to never mix them up again.
❓SQL · October 6, 2026 · 4 min
SQL isn't programming: it's asking questions
If you can ask “how many students passed?”, you already know half of SQL. We'll teach you the other half.