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SQL

The language of data. Queries, joins, indexes, and patterns.

Browse 7 tutorials → Other topics

Why learn SQL?

  • Almost every backend touches a relational database.

  • A skill that has stayed valuable for 50+ years and still will.

  • Declarative — describe what you want, not how to compute it.

  • Transferable across Postgres, MySQL, SQLite, and dozens of dialects.

What you can build with SQL

Querying production data for product, analytics, and ops Designing schemas for application backends Reporting and dashboards Data engineering pipelines

SQL tutorials

7 articles

Hand-written tutorials, ordered as a recommended learning path.

  1. 01 What Is SQL? A clear, no-hype introduction to SQL — what relational databases are, why declarative querying matters, the main dialects, and when SQL beats spreadsheets or NoSQL.
  2. 02 SELECT Basics A practical introduction to SELECT, FROM, WHERE, ORDER BY, LIMIT, and DISTINCT — with a running users and orders dataset so every query has real meaning.
  3. 03 GROUP BY Summarise data the right way — COUNT, SUM, AVG, MIN, MAX, GROUP BY across one or many columns, and the WHERE vs HAVING distinction that catches everyone the first time.
  4. 04 Normalization A practical guide to database normalization with real customer and order examples. Covers 1NF, 2NF, 3NF, when to denormalize, and tradeoffs.
  5. 05 Transactions Understand SQL transactions, ACID guarantees, isolation levels from read uncommitted to serializable, and the concurrency anomalies they prevent.
  6. 06 Window Functions Learn SQL window functions with practical examples. Covers ROW_NUMBER, RANK, DENSE_RANK, LAG, LEAD, running totals, and the OVER clause in depth.
  7. 07 Postgres EXPLAIN Learn how to read Postgres EXPLAIN and EXPLAIN ANALYZE output, spot expensive operations, and apply practical indexing and rewrite techniques to speed up queries.