PostgreSQL

Ask questions of a real PostgreSQL database, from your first SELECT to schema design. 21 modules of 10 minutes each, with questions that check your answers in the browser.

Start the track

Foundations

• 1. What a relational database is: tables, rows, columnsFree
  Meet the database you'll use all track long, and learn the words everyone uses to talk about tables.
• 2. SELECT and FROMFree
  Ask for exactly the columns you need, in the order you want, and read the result like a pro.
• 3. WHERE and comparison operatorsFree
  Keep only the rows you care about, combine conditions safely, and avoid the AND/OR trap that silently breaks reports.
• 4. ORDER BY and LIMITFree
  Sort results the way people read them, get the top N rows, page through results, and avoid the tie trap.
• 5. DISTINCT and basic expressionsFree
  Remove duplicate rows, calculate new columns like profit margins, and dodge the integer-division trap.

Intermediate

• 6. Aggregate functions (COUNT, SUM, AVG)Free
  Turn many rows into one answer: how many, how much, on average, the smallest and the largest.
• 7. GROUP BY and HAVINGFree
  Compute totals per category, per customer or per month, and filter groups with HAVING.
• 8. Aliases and CASE expressionsFree
  Name things clearly, label rows with if/then logic, and count several things in one pass with conditional aggregation.
• 9. INNER JOINPro
  Combine tables through their keys so an order shows its customer's name and its products, and avoid double counting.
• 10. LEFT / RIGHT / FULL joinsPro
  Keep rows that have no match, find what's missing, join a table to itself, and avoid the WHERE clause that secretly undoes a LEFT JOIN.
• 11. Handling NULLs (COALESCE, IS NULL)Pro
  Understand why NULL breaks normal logic, find and replace missing values, and avoid the NOT IN trap and division-by-zero errors.
• 12. Text functions and pattern matching (LIKE, ILIKE)Pro
  Search text with patterns, clean messy names and emails, and split text into parts.
• 13. Dates and timesPro
  Group sales by month, measure days between events, filter date ranges safely, and format dates for reports.

Advanced

• 14. SubqueriesPro
  Use the answer of one query inside another, with IN, EXISTS, correlated subqueries and derived tables.
• 15. Common Table Expressions (WITH)Pro
  Break big queries into named, readable steps, and walk hierarchies with recursive CTEs.
• 16. Window functions (ROW_NUMBER, RANK, running totals)Pro
  Rank rows, compute running totals and month-over-month changes, and pick the top N per group, all without losing rows.
• 17. Combining results: UNION, INTERSECT, EXCEPTPro
  Stack query results on top of each other, and find what two lists share or what one has that the other doesn't.
• 18. Creating tables, data types, and constraintsPro
  Design tables that refuse bad data, with the right types, primary and foreign keys, NOT NULL, UNIQUE, CHECK and defaults.
• 19. INSERT, UPDATE, DELETEPro
  Add, change and remove rows safely, return what changed, and upsert with ON CONFLICT.

Expert

• 20. Indexes and reading a query plan (EXPLAIN)Pro
  Learn how the database finds rows fast, read EXPLAIN output, and write queries that can use indexes.
• 21. Transactions, normalization, and schema designPro
  Make multi-step changes all-or-nothing, spot badly designed tables, and design a clean schema from scratch.

Track project

• SQL Project: Toko Kita's reporting queriesPro
  Three graded queries on the shop's real database. Find the best customers for a thank-you campaign, build a monthly revenue report with a running total, and write the restock report the warehouse checks every Monday.

Pro modules unlock with one payment of Rp 149.000, yours to keep.