SQL Data Analysis

Description

Company data lives in databases, and the fastest way to an answer is a query. But SQL has a nasty habit: a query can run without an error and still return the wrong number. This course teaches you to write SQL that is correct, readable and checked, and it is built around the mistakes that produce wrong results silently: the average that ignores NULL, the join that multiplies rows, the filter that quietly turns a left join into an inner join, the NOT IN that returns nothing.

What you will learn

• Query, filter and sort, and understand the order in which SQL really evaluates a statement.
• Handle NULL, expressions, dates and text with confidence, and check every result for grain, totals and samples.
• Aggregate with GROUP BY and HAVING, build rates and shares with conditional aggregation and rank groups.
• Join tables without fan-out, use anti-joins and set operations, and structure hard questions with subqueries and CTEs.
• Use window functions for rankings and running totals, and build cohort retention and funnel analyses.

A database on your own machine

There is no server to install and no account to create. The data is a single SQLite file, the online shop Trailhead Outfitters with 1,200 customers, 40 products, about 5,900 orders, their order lines and 29,540 website sessions, and you open it from Python in Google Colab or Jupyter. Because the data is the same shop as in the first course of the path, you already know what the numbers should look like, which makes checking a query easier.

How the lessons work

Each lesson explains an idea with a short piece of theory (including the relational reasoning behind it), then shows real queries with their real results, then gives exercises with hints. You are encouraged to treat every query as a claim that needs a check, and you practice the checks: row counts, totals that must add up and independent computations.

The project

The last module is a guided project: a customer and revenue analysis written entirely in SQL for a leadership meeting. It covers revenue by category and channel, customer value, cohort retention and the buying funnel. You get a brief, a starter notebook with ten milestones and 20 self-checks (it opens the database read-only, like a careful analyst working on production), and a worked solution to compare with.

What is included

Lessons on querying, aggregation, joins and window functions, ready-to-use SQLite data of the whole shop, a guided customer and revenue project with starter and solution notebooks, and a quiz for every module.

Who it is for

SQL is the skill that opens the most doors in data work, and most people learn it badly, from tutorials that never show what goes wrong. This course shows you exactly that, so your queries are trusted and your numbers hold up when someone checks them. If you work with company data, or want to, and you are done with wrong totals and mystery duplicates, this is the course to take. Enroll now and start writing queries you can stand behind.