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Foundations: spreadsheets, data literacy and first SQL · Novice · Lesson 11 of 99 · 8 min video, then about 1 hour of practice
How relational databases organise data: tables, keys and relationships
After this you can read a database schema, identify primary and foreign keys, and predict how two tables relate (one-to-one, one-to-many, many-to-many).
Why it matters
SQL makes sense once you see a database as a set of linked tables. Understand primary keys (what makes a row unique), foreign keys (how one table points to another) and relationship cardinality. That knowledge is what lets you predict whether a join will multiply rows, which is the source of most wrong numbers in analyst SQL.
How to use this resource
A concise explanation of what a relational database is and why data is split into related tables.