---
title: "Indexes in DB2 These 3 are Must Know Rules"
description: "Index is popular object in DB2 SQL. Popular questions to your instant knowledge given for quick reference."
url: https://srinimf.com/2018/02/20/db2-index-questions/
date: 2018-02-20
modified: 2022-07-29
author: "Srini"
image: https://i0.wp.com/srinimf.com/wp-content/uploads/2018/02/pexels-photo-7129700.jpeg?fit=1880%2C1253&ssl=1
categories: ["Categories", "DB2"]
tags: ["DB2 Index", "Db2 Tips", "SQL tips and tricks"]
type: post
lang: en
---

# Indexes in DB2 These 3 are Must Know Rules

The index improves the performance of the search. The index looks like a keyword at the end of a book. Here are three must-know points.

## 1.Uniqueness

You can create indexes on a table. The UNIQUE keyword in creating an index enforces uniqueness when you enter data. That means it will not allow [duplicate entries on that column](https://srinimf.com/2018/01/14/db2-logical-storage-theory-to-define-when-creating-table/). It is the main benefit of UNIQUE.

## 2. Index on an Empty Table

**The second point.**

**What will happen if you create an index on an empty table?** There will be no entry in the index table.

## 3. Index on Non-empty Table

**What will happen when you create an index on a table which is non-empty?** Then, the Index-table will have entries.

**The index disadvantage**

If a large number of indexes you create for a table is modified frequently, overall performance will decrease.  

***References and resources***

- [Here’s You Can Practice DB2 Online ](https://www.ibm.com/developerworks/downloads/im/db2express/)
- [Three minute SQL Quiz](https://srinimf.com/2017/11/06/three-minute-sql-quiz-prove-your-knowledge/)

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