INTERACTIVE LECTURES
Understand database structure
Guided class activity · apply the ideas from the full SQL lessons.
Opening your saved work…
Sign in to save across devices → · Download your guest work before switching accounts.
Identify entities and keys
Step 1 of 3 · Database: Northshore Coffee
READ & UNDERSTAND
A table groups facts about a type of entity or event. In this database one shops row represents a shop, one employees row an employee, and one orders row an order.
A primary key identifies a row. A name is often a poor key because names can repeat or change. Keep the identifier and the human-readable label separate.
An ERD should label the entities, keys, and relationship cardinalities. The database explorer shows declared keys; business rules require explanation beyond the diagram.
Worked example
SELECT id, name, city FROM shops ORDER BY id;
The shop id is the stable row identifier, while name and city make the result understandable. Several shops can share a city without representing the same shop.
The employee exercise deliberately includes shop_id beside employee id. Identifiers with the same numeric value are not interchangeable when they refer to different tables.
Your question
Return id, first_name, last_name, and shop_id for the first five employees ordered by id.
Explain your evidence
Which field identifies the employee? Which connects that employee to a shop?
Try a query to unlock the worked-answer discussion.
Query results
Predict the result, then run your query.Predict the result, then run your query.
Read-only activity · One statement per run · First 200 rows displayed · Checks compare the complete bounded result, not just this preview.
Explore this query freely in the playground ↗Check the save status above. Account-saved work is available in My Progress. Explanations are for discussion, not automatically graded. No prerequisite locks.