SQL Fundamentals · Joins · Lesson 12 of 17
Why Joins?
Concept
Why Joins?
Relational data is split across multiple tables to avoid repetition. A JOIN combines rows from two tables based on a shared column.
By the end of this lesson
- Explain the core idea behind Why Joins?.
- Predict output before running a change.
- Test one realistic and one unusual input.
- Use the result to make the next decision.
How to study this page
- 1. Read one concept.
- 2. Change the example.
- 3. Run, compare, and explain.
- 4. Complete the challenge below.
Self-check before continuing
Without looking at the example, describe what changes when you modify one input in Why Joins?. Then reopen the editor and prove your explanation with a small test.
You are ready to continue when you can predict, test, and explain the result.
Your turn
Explain, as a comment, why storing enrollments in a separate table avoids duplicating student data.
Need a nudge?
Ask about this lesson or your next move. The guide explains the path without taking the work away from you.
Ready for the next lesson?
Mark this lesson complete when you have finished the exercise.
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