Indexing 

Indexing ek technique hai jo database ke data ko fast search karne mein help karti hai — jaise book ke end mein index hota hai, jisse aap kisi topic ka page number directly dekh sakte ho.

Agar index nahi hoga to database ko har row ek-ek karke check karni padegi (isko full table scan bolte hain) — jo slow hota hai.

 Index = Fast searching
No Index = Slow searching

 Real-Life Example

Sochiye aapke paas ek phone directory hai:

• Agar index nahi hai to aapko har page dekhna padega kisi naam ke liye.

• Agar index hai to aap seedha “S” section pe jaa sakte ho “Suresh” dhoondhne ke liye.

SQL Indexing bhi aise hi kaam karta hai — directly relevant data tak pahuch jaata hai.

 Indexing kaise kaam karta hai

Jab aap kisi column par index create karte ho, DBMS ek alag data structure banata hai (jaise B-Tree ya Hash Table) jisme:

• Column ki values hoti hain

• Un values ki pointer hoti hai original row tak

 Employees Table Example

Agar hum Name column par index banate hain:

 Index Table

Ab query:

Direct Row 3 par jaayegi — fast!

 Types of Indexes

1. Single Column Index

Ek column par banta hai:

2. Composite Index

2 ya usse zyada columns pe:

3. Unique Index

Duplicate values allow nahi karta:

4. Primary Key Index

Jab aap primary key banate ho to DBMS automatically index bhi bana deta hai.

 Indexing ke Fayde

 Indexing ke Nuksaan

 Example – Query Speed with Index

Suppose Students table mein 1 million rows hain:

Without index:

 Full table scan — slow

With index:

 Index scan — super fast

 Diagram: Indexing Concept

 Kab Index Use Karna Chahiye?

Index Use Karo jab:

• WHERE clause mein bar bar use ho raha ho

• Column foreign key ho

• Table bahut bada ho

Index ko avoid karo jab:

• Table chhoti ho

• Column mein zyada duplicate values ho (like gender)

 Summary Table