---
title: "What is Index? Types of Index in SQL Server"  
description: "What is Index? Types of Index in SQL Server"  
author: "Anubhav Sharma"  
published: 2026-03-15  
updated: 2026-04-05  
canonical: https://www.mindstick.com/forum/162064/what-is-index-types-of-index-in-sql-server  
category: "SQL Server"  
tags: ["sql server"]  
reading_time: 3 minutes  

---

# What is Index? Types of Index in SQL Server

**What is [Index](https://www.mindstick.com/blog/198/index-in-sql-server)? Types of Index in [SQL Server](https://www.mindstick.com/articles/12999/what-is-table-valued-function-in-sql-server)**

## Replies

### Reply by ICSM Computer

An **Index** in [SQL](https://www.mindstick.com/articles/13115/types-of-keys-in-sql-or-oracle-database) [Server](https://www.mindstick.com/articles/43769/what-is-serverless-architecture-is-it-worth-switching-over) is a database object that **improves the speed of data retrieval** from a table—just like an index in a book helps you quickly find a topic without scanning every page.

In Microsoft SQL Server:

> An index creates a **sorted structure (like a tree)** that allows fast searching, filtering, and sorting of data.

## Why Use Indexes?

- Faster `SELECT` queries
- Efficient searching and filtering
- Improves `JOIN`, `ORDER BY`, `GROUP BY` performance

But:

- Slows down `INSERT`, `UPDATE`, `DELETE`
- Takes extra storage

## Types of Indexes in SQL Server

### 1. Clustered Index

- Physically sorts and stores the data in the table
- Only **one clustered index per table**
- Data rows are stored in order of the index key

## Example:

```plaintext
CREATE CLUSTERED INDEX IX_Employee_Id
ON Employee(Id);
```

## Use Case:

- Primary key columns
- Frequently sorted or range queries

### 2. Non-Clustered Index

- Does **not change physical order** of table
- Creates a separate structure with pointers to data
- You can have **multiple non-clustered indexes**

## Example:

```plaintext
CREATE NONCLUSTERED INDEX IX_Employee_Name
ON Employee(Name);
```

## Use Case:

- Frequently searched columns
- Filtering (`WHERE Name = 'John'`)

### 3. Unique Index

- Ensures all values in the column are **unique**
- Prevents duplicate entries

## Example:

```plaintext
CREATE UNIQUE INDEX IX_Email
ON Users(Email);
```

### 4. Composite Index (Multi-Column Index)

Index on **multiple columns**

## Example:

```plaintext
CREATE INDEX IX_Name_Department
ON Employee(Name, Department);
```

## Use Case:

- Queries using multiple columns in `WHERE` clause

### 5. Filtered Index

- Index on a **subset of data**
- Smaller and faster than full index

## Example:

```plaintext
CREATE INDEX IX_ActiveUsers
ON Users(IsActive)
WHERE IsActive = 1;
```

### 6. Full-Text Index

- Used for **searching text data** (large text fields)
- Supports complex queries like word matching

### 7. Columnstore Index

- Stores data **column-wise instead of row-wise**
- Best for analytics and reporting

## Use Case:

- Large datasets
- Data warehousing

### 8. XML Index

Used for querying XML data efficiently

### 9. Spatial Index

Used for geographic or spatial data

## Clustered vs Non-Clustered (Quick Comparison)

| Feature | Clustered Index | Non-Clustered Index |
| --- | --- | --- |
| Data Storage | Physically sorted | Separate structure |
| Count | One per table | Multiple allowed |
| Speed | Faster for range queries | Faster for lookups |

## When to Use Indexes

- Columns used in `WHERE`, `JOIN`, `ORDER BY`
- Frequently queried columns
- Large tables

## When NOT to Use

- Small tables
- Frequently updated columns
- Too many indexes (can reduce performance)

## Simple Analogy

- **Clustered Index** → Like a dictionary (data is sorted A–Z)
- **Non-Clustered Index** → Like a book index (points to page numbers)


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Original Source: https://www.mindstick.com/forum/162064/what-is-index-types-of-index-in-sql-server

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