From idea to schema
The café wants online table bookings: guests book a table for a time and party size. Design the tables with the right keys and constraints, add sample data, and answer a question with a JOIN.
Test the rules with bad data
Once the schema exists, try to break it on purpose. Insert a booking for a guest id that doesn't exist, a party of zero, and two bookings for the same table and time. Each insert should fail with a clear constraint error. If one succeeds, a rule is missing.
This habit of testing the unhappy paths is how real teams gain confidence in a schema before any app code depends on it.