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Core skills: building for the web · Advanced beginner · Lesson 23 of 98 · 2 h 53 min video, then about 1 week of practice
SQL and PostgreSQL
After this you can write SELECT queries with joins, filters, grouping and aggregates, and insert, update and delete rows safely.
Why it matters
Relational databases hold most of the world's important data, and SQL has outlived every technology that was supposed to replace it. You need to be genuinely fluent: joins, grouping, aggregates, subqueries, and transactions. Practise on real exercises, not just videos. SQL is learned by writing queries. Trap: only ever using an ORM. ORMs are useful, but when a query is slow or wrong you will need to read and write the SQL it generates.
How to use this resource
A thorough PostgreSQL course. Type every query yourself.