Part 04 Constraints: Did you know Unique key optimize search by using index called B Tree

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One missing constraint cost me real data
in production.

Don't let it happen to you.

In this short I break down what SQL
constraints actually are, why every
serious database needs them, and show
you a real example in under 60 seconds.

📁 Full notes and examples FREE on GitHub
→ github.com/nitin-cse

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⚡ WHAT ARE SQL CONSTRAINTS?

Constraints are rules you set on your
database columns to protect your data
from bad values, empty fields, duplicates,
and broken relationships.

Without constraints your database will
accept anything you throw at it.

With constraints your database says NO
before bad data ever gets stored.

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🛡️ THE 5 ESSENTIAL CONSTRAINTS

NOT NULL
→ Column cannot be empty
→ No more missing required fields

UNIQUE
→ No duplicate values allowed
→ Protects emails, usernames, IDs

CHECK
→ Value must pass your rule
→ price greater than 0, age BETWEEN 18 AND 99

PRIMARY KEY
→ Every row has a unique identity
→ NOT NULL + UNIQUE combined

FOREIGN KEY
→ No orphaned relationships
→ Child row must have valid parent

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⚠️ THE GOTCHAS NOBODY TELLS YOU

→ CHECK constraints let NULL pass silently
→ SERIAL does NOT guarantee NOT NULL
→ UNIQUE allows multiple NULLs
→ Missing WHERE on DELETE wipes everything
→ CASCADE on FOREIGN KEY deletes children

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📁 FREE GITHUB NOTES

All 5 constraints documented with:
→ Real working examples
→ Before and after result tables
→ Common mistakes and fixes
→ Production ready patterns

Give it a star if it helps you 🌟
→ github.com/nitin-cse

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📚 FULL SERIES — PostgreSQL from Zero

→ Day 01 — What is SQL
→ Day 02 — Database and RDBMS
→ Day 03 — CHECK and NULL loophole
→ Day 04 — SERIAL vs IDENTITY
→ Day 05 — EXCLUSION constraints
→ Day 06 — ON DELETE behaviours
→ Day 07 — CASCADE nuclear option
→ Day 08 — All 5 constraints ← YOU ARE HERE
→ Day 09 — Table modification
→ Day 10 — SELECT mastery

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🔔 FOLLOW THE JOURNEY

I am Nitin — Senior Data Engineer
in Dublin, Ireland.

Learning PostgreSQL in public every
single day and documenting everything
for free so you don't have to figure
it out alone.

Subscribe for daily PostgreSQL Shorts 🔔

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