Full Stack Open 2025
A deep dive into modern JavaScript-based web development: React, Redux, Node.js, GraphQL, TypeScript, CI/CD and containers. Self-paced, project-driven, with optional ECTS credits.

Rating ⭐️ 4.7 / 5 (33 Class Central reviews)

Students 👨‍🎓 11.1 K

Duration ⏰ Self-paced (~200 hrs total)

Created by 👨‍🏫 Matti Luukkainen, Kalle Ilves & Jami Kousa (University of Helsinki)

🔗 COURSE LINK: https://fullstackopen.com/en/

🔹 SQL Series: Day 6️⃣ – Mastering the Primary Key

👋 Hey data adventurers! Today we’re shining the spotlight on the Primary Key - the VIP pass that makes every row unique and lightning-fast to find.

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🛠 Origins: Why Primary Keys Were Born

* Prevent Duplicate Records: In early systems, it was all too easy to accidentally insert “two Alices” primary keys ensure each record stays one-of-a-kind.
* Enable Fast Access: As datasets grew, scanning millions of rows was impractical. Keys provided a built-in index for instant lookups.
* Support Relationships: To link data across tables reliably (think Orders → Customers), you need a stable, unique anchor.

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+----+---------+-----------------------+  
| id | name    | email                 |  
+----+---------+-----------------------+  
| 1  | Alice   | [email protected]     |  
| 2  | Bob     | [email protected]       |  
| 3  | Carol   | [email protected]     |  
+----+---------+-----------------------+  

🔑 What Makes a Primary Key Special?

* Unique – No two rows share the same value.
* Not NULL – Every record must have one.
* Indexed – The database auto-builds an index, so WHERE id = 2 is blazing fast.
* Integrity Enforcer – Prevents duplicates and anchors foreign-key relationships.

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📋 1. Only One per Table
A table can have just one primary key.

> Even if it’s made of multiple columns (a composite key), you still pick *one* PK to enforce uniqueness.

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🧩 2. Composite Primary Keys
When no single column does the job, team up two (or more) columns:

PRIMARY KEY (order_id, product_id)

This combo ensures each row is unique only when both values match.

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🌱 3. Natural vs. Surrogate Keys
Primary key can be natural or surrogate key:
* Natural Key: Real-world data (e.g., email).
* Surrogate Key: System-generated (e.g., AUTO_INCREMENT or a UUID).

> Tip: Surrogates stay stable; naturals can change (and bite you!).

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🛡 4. Best Practices
• Stable – Pick values that won’t change.
• Minimal – Keep it short; every byte counts.
• Simple – One-column PKs are easiest; use composites only when needed.

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🔐 While the Primary Key is our star today, remember there’s a whole key family waiting in the wings: Super Keys, Candidate Keys, Alternate Keys, Composite Keys, Unique Keys, Foreign Keys, Surrogate Keys… we’ll dive into those soon!

Bash brackets cheat sheet

For all those bash people out there, this might be useful

Man gotta love bash, right? 😁