Скачать или смотреть Primary Key vs Unique vs Indexes 🔥 | SQL Server Hindi Class – Null, Not‑Null & Clustered Explained

📊 *SQL Server Constraints & Indexes – Full Hindi Class*
इस सेशन में हम LIVE टेबल बनाकर Primary Key, Unique constraint, Null/Not‑Null, Clustered‑vs‑Non‑Clustered Indexes और Identity columns को step‑by‑step समझते हैं।

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⏱️ *Chapters*
0:00 Intro – Creating SALES table
1:14 What is a PRIMARY KEY? (Business Integrity rules)
4:53 Why you can have only ONE Primary Key per table
7:06 UNIQUE constraint demo (multiple allowed)
9:55 Null vs Not‑Null with UNIQUE key
14:15 Automatic Clustered Index on Primary Key
16:40 How many Clustered indexes can a table have?
19:00 Creating additional Non‑Clustered indexes
24:00 UNIQUE + Null behaviour illustrated
29:40 Real‑world phone‑number example
33:00 Identity column concept
34:50 Quick recap & Q&A

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🔑 *Key Takeaways*
• Difference between PRIMARY KEY & UNIQUE
• Why PRIMARY KEY ⇒ Not‑Null + Clustered Index auto‑created
• UNIQUE allows multiple Nulls? (demo & edge cases)
• Only 1 Clustered Index per table, many Non‑Clustered
• Identity(1,1) for auto‑increment IDs

💾 **Script & Notes**:
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💻 *Commands Used in Video*

-- Create SALES table
CREATE TABLE SALES (
ID INT PRIMARY KEY,
ProductName VARCHAR(100),
PhoneNumber VARCHAR(15) UNIQUE,
Quantity INT NOT NULL
);

-- Add UNIQUE constraint
ALTER TABLE SALES ADD CONSTRAINT UQ_Phone UNIQUE (PhoneNumber);

-- Add Non-Clustered Index
CREATE NONCLUSTERED INDEX IX_SALES_Quantity ON SALES(Quantity);

-- Identity column example
CREATE TABLE EMPLOYEE (
EmpID INT IDENTITY(1,1) PRIMARY KEY,
EmpName VARCHAR(100)
);


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