PostgreSQL & MySQL
The open-source relational databases behind most web applications, and SQL practice.
Beginner
Start here. No background needed beyond school maths.
PostgreSQL Tutorial
Step-by-step lessons on SQL in ••••, from selecting and filtering to joins, window functions, indexes and stored procedures.
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SQL Tutorial (ThoughtSpot, formerly Mode)
A SQL course aimed at analysts, with a basic, intermediate and advanced track and real data to practise on.
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MySQL Tutorial
MySQL's own walkthrough: connect, create tables, load data and run the queries you will use every day.
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Advanced
Once the basics are comfortable.
PostgreSQL EXPLAIN Glossary
Reads like a dictionary for query plans: what each node in EXPLAIN output means and what to look for when a query is slow.
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PostgreSQL Wiki: Don't Do This
A short list of common •••• mistakes and what to do instead, from choosing data types to using timestamps and NULL correctly.
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