Real SQL.
Real results.
Write against live Postgres sandboxes, get auto-graded in milliseconds, and progress through six structured courses — from SELECT to window functions and CTEs.
Curriculum
Six courses. Clear progression.
From your first SELECT to window functions and CTEs — each builds on the last.
SQL Fundamentals
Write your first real queries — pick columns, filter rows, sort results, and limit output. The four moves you will use in every query you ever write.
What you'll learn
- ✓Write your first SELECT queries
- ✓Filter, sort & limit results
- ✓Alias tables and columns
Filtering & Logic
Stop returning too many rows. Master WHERE clauses with AND, OR, LIKE, IN, BETWEEN, and NULL handling — the difference between a query that works and one that almost works.
What you'll learn
- ✓Master AND / OR / NOT logic
- ✓Use IN, BETWEEN, LIKE, IS NULL
- ✓Build multi-condition filters
Aggregations & Grouping
Turn thousands of rows into meaningful numbers. COUNT, SUM, AVG, GROUP BY, and HAVING power every dashboard and business report you will ever build.
What you'll learn
- ✓COUNT, SUM, AVG, MIN, MAX
- ✓Group rows with GROUP BY
- ✓Filter groups using HAVING
Joins
Query multiple tables at once. Master INNER, LEFT, RIGHT, and FULL OUTER joins — and finally understand which rows appear in your result and why.
What you'll learn
- ✓INNER, LEFT, RIGHT & FULL joins
- ✓Join tables on matching keys
- ✓Multi-table queries
Subqueries & CTEs
Break hard questions into readable steps. Subqueries and WITH blocks let you compose multi-stage logic that would be impossible — or unreadable — in a single query.
What you'll learn
- ✓Scalar & correlated subqueries
- ✓Build reusable CTEs with WITH
- ✓Nested query logic
Window Functions
The most powerful feature in SQL — and the most asked-about in data interviews. Rank rows, run totals, and compare each row to its neighbors without collapsing your result set.
What you'll learn
- ✓RANK, ROW_NUMBER, DENSE_RANK
- ✓Running totals with SUM OVER
- ✓LAG, LEAD & NTILE
How it works
Read. Write. Get graded.
The fastest way to build SQL fluency is doing, not watching. Each lesson ends with real exercises.
Read the concept
Short, focused lessons with real examples — written for analysts and engineers, not academics.
Write real SQL
Execute against live Postgres sandboxes. See real rows, real errors, real timing.
Get graded instantly
Auto-grading compares your output to the expected result in milliseconds. Pass and move forward.
Practice data
Three real sandbox databases
Realistic relational schemas with seeded rows — switch between them instantly.
HR Database
Enterprise HR schema. Practice aggregations, salary analytics, org hierarchies, and window functions.
Store Database
Retail e-commerce schema. Revenue rollups, customer RFM segmentation, basket analysis, and inventory queries.
Hospital Database
Healthcare schema. Appointment funnels, doctor performance dashboards, and patient visit analysis.
Start today · Build real SQL fluency
The SQL skills that get you hired — and promoted.
LearnWithSQL gives you a complete path: structured courses, a free sandbox playground, 86+ graded exercises, and a full SQL reference — all backed by real PostgreSQL.