Relational thinking: tables, keys, relationships
By the end of today you can turn a description of a business into tables with keys and relationships, and explain why storing the same fact in two places will eventually make them disagree.
YesterdayOn Day 5 you chose collections for data in memory. Today you choose structures for data that must survive the process ending.
TomorrowTomorrow you query these tables and find out whether your model was any good.
Why this matters
Schema decisions outlive every framework choice you will make. A bad schema is felt every day for years; a good one makes queries obvious.
- Tables and rows
- Keys
- Relationships
- Storing a fact once
Learn it
75 minCopy this into Claude or ChatGPT. It quizzes you before it explains anything, which is deliberate. The resources under it are how you check what it told you.
Today's Master Prompt
Free · sign inA prompt written for this day alone: your level, the exact scope, what to leave out, and an instruction to quiz you before it explains anything. Paste it into Claude or ChatGPT and it teaches you today's material.
Check it against something that is not a model
An assistant can be fluent and wrong, and on a topic you met today you will not catch it. These cover the same ground and were made by people who do this for a living, so they are what you hold the explanation up against. They are other people's work and we only link to them, so judge them for yourself.
4 hand-picked resources
Free · sign inVideos, official docs and articles covering the same ground, each opened and annotated by hand. They are what you check the assistant against on a day you cannot yet catch it being wrong.
Build it
50 minDesign a schema for a library with books, copies, members and loans, where a book can have several physical copies and a member can borrow many over time. Write the CREATE TABLE statements with keys and constraints, and create it in a real Postgres database. Then write one paragraph on which facts are stored exactly once and where you were tempted to duplicate.
Recall it
20 minAnswer out loud, reveal, then mark honestly whether you had it. That score is the only thing on this page you do not get to choose.
5 recall questions
Free · sign inQuestions you answer from memory, then grade yourself against the real answer. The score is carried into the mastery rating below it, so an honest miss cannot quietly become a tick.
Rate it
Completion and mastery are tracked separately. Be honest, because an inflated rating only means the concept resurfaces sooner.
Mastery tracking
Free · sign inRate yourself against five named criteria per concept. Completion and mastery are tracked separately, and anything you rate shakily comes back automatically on a spaced schedule.
Recap
- 01A table has a fixed shape; a dict does not, and that constraint is the point
- 02Many-to-many always needs a third table
- 03Store each fact once, or watch the copies drift apart
- 04NULL means unknown, and it makes every reader ask what that means
Your progress
Free · sign inMark days complete, pick up where you left off across devices, and watch completion and mastery diverge. Free, and the account exists only so ninety days of work cannot vanish with a cleared browser.