Data Janitor: The Cleanup Crew
Inherit a filthy table full of duplicates, NULLs, and typos, then write the queries that find and fix every data-quality crime.
What you'll be able to build
Inherit a filthy table full of duplicates, NULLs, and typos, then write the queries that find and fix every data-quality crime. Along the way you pick up real, transferable SQL skills, not just this one project:
- NULL handling (IS NULL, COALESCE, NULLIF) and why NULL breaks comparisons
- Deduplication: finding dupes with GROUP BY ... HAVING COUNT(*) > 1
- Picking the survivor row per group with ROW_NUMBER() in a CTE
- Normalizing text (TRIM, LOWER, REPLACE) for consistent grouping
- CASE expressions to standardize/categorize messy values
- CAST and type-coercion pitfalls when columns hold mixed data
A course like this one
Yours is built from your own placement, so module count and depth will differ. This map shows what a intermediate-level SQL learner building Data Janitor actually gets.
- Module 1: Tables, Rows, and Query Intent5 lessons
Builds the table model for your data janitor.
- Module 2: Joins, Groups, and Data Shape5 lessons
Builds the join shape workflow for your data janitor.
- Module 3: Filters, Conditions, and Result Sets5 lessons
Builds the filter rule that powers your data janitor.
- Module 4: Reusable Query Patterns5 lessons
Builds the reusable query helper for your data janitor.
- Module 5: Transactions and Data Boundaries5 lessons
Builds the transaction boundary for your data janitor.
- Module 6: Reliable Reporting Queries3 lessons
Builds the report query for your data janitor.
How the lessons actually work
Every lesson has you predict what a piece of SQL code will output before you run it, then run it for real in your browser and fix what you got wrong. Each module ends in a challenge gate with hidden tests, so you can't advance until your code actually works. The course closes with a capstone that assembles everything into Data Janitor, and a runnable proof page tied to your own code.
Common questions
How long does the Data Janitor: The Cleanup Crew course take?
about 7 hours, across 6 modules and 28 lessons, at roughly 15 minutes per lesson. Your own course may run shorter or longer, since it's sized to your placement result, not a fixed template.
Do I need experience?
Some. This is an intermediate-tier SQL project, so it assumes you're comfortable with SQL basics and pushes past them.
How much does it cost?
$15 one-time, no subscription. The first module is free, so you can see exactly how the course teaches before you pay for the rest.