SQL Tutorial: How to Calculate Month-over-Month Growth Using LAG()

Data analyst Michael Nocito published a technical tutorial on August 7, 2026, explaining how to write reliable month-over-month growth queries in SQL. The guide covers the core growth formula — current month minus prior month, divided by prior month — and how the LAG() window function retrieves the previous row's value. Nocito highlights three common traps that silently produce wrong results: integer division, an empty first month, and missing months in the data. The critical distinction he emphasizes is that LAG() fetches the previous row, not the previous calendar month, meaning a gap in the data causes it to compare non-adjacent months. All examples were tested in SQLite using a 12-row dataset deliberately missing April, making it reproducible on any machine running SQLite 3.25 or later.