---
title: "DB2: Unique-index Vs Clustered-index"
description: "Indexes improve the performance of the database tables. However, this post covers differences between clustered index and unique index."
url: https://srinimf.com/2020/09/13/db2-unique-index-vs-clustered-index/
date: 2020-09-13
modified: 2026-10-10
author: "Srini"
image: https://i0.wp.com/srinimf.com/wp-content/uploads/2020/09/pexels-photo-4494642.jpeg?fit=1880%2C1253&ssl=1
categories: ["DB2"]
tags: ["DB2 Unique Vs Clustered index"]
type: post
lang: en
---

# DB2: Unique-index Vs Clustered-index

The index on a table improves performance. In other words, an indexed Table takes less CPU time. And that fetches results faster. Here I am sharing differences between clustered index and Unique-index.

Related[Teradata Unique Secondary Index USI](https://srinimf.com/2014/11/28/teradata-unique-secondary-indexusi/)

## Unique Index

Let me explain it with an example, the column that you use for the UNIQUE index may not be NOT NULL.

Related[SQL Index Vs Database Index: Top Differences](https://srinimf.com/2016/10/08/the-best-differences-sql-index-and-database-index/)

The uniqueness you always expect from the UNIQUE index. So it does not allow duplicates.

Moreover, you can create **multiple** UNIQUE indexes on a Table.

Related[DB2: List of 7 Top Indexes](https://srinimf.com/2010/07/24/db2-indexes/)

**Example**

Related[Logging in IMS DB: A Complete Guide to Audit Trail Records](https://srinimf.com/2016/09/30/3-strong-reasons-why-logging-in-ims-db-needed/)

```
CREATE UNIQUE INDEX ORD_INDX
ON ODER_TABLE (ORDER_NUMBER);
```

## Clustered Index

Only **one index** in a table can be a clustered index. It tries to store records on a page that has similar index keys/values. And it is designed to increase performance by decreasing I/O.

In terms of quantity, you can create only one Clustered index on a Table.

**Example**

```
CREATE UNIQUE INDEX ORD_INDX
ON ODER_TABLE (ORDER_NUMBER)
CLUSTER;
```

Related Posts

- [DB2 Index Vs. Hash Scan: Top Differences](https://srinimf.com/2018/11/01/db2-top-differences-read-on-index-vs-hashing/)DateNovember 1, 2018
- [DB2 SQL: How to Create Index (1 of 2)](https://srinimf.com/2015/08/09/db2-different-sql-queries-for-creating-index-1-of-2/)DateAugust 9, 2015
- [DB2: List of 7 Top Indexes](https://srinimf.com/2010/07/24/db2-indexes/)DateJuly 24, 2010

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