SQL for Real-World Analysis

Your query runs, the totals look plausible, and then someone shows you a different number. This book teaches the habits that stop that from happening. Through one fictional online shop, you learn to define the question and the grain before you write any SQL, profile messy columns, and clean them inside the query so the fix is visible. You then join tables without double counting, aggregate correctly around missing values, handle dates, time zones and customer cohorts, and use window functions for comparisons. Finally you make queries readable, test them, reconcile results and present findings with honest caveats. Examples use standard SQL, with dialect differences noted and summarized in a quick reference. Written for analysts, operators and students who want numbers they can defend.