MySQL Table Indexing: A Complete Beginner’s Guide

When a database table grows large, searching for data can become slow and inefficient.
Imagine searching for a name in a 1000-page book without an index—you would have to read every page.

👉 Table indexing in MySQL solves this problem by making data searches fast and efficient.

This guide explains what indexing is, why it’s important, how it works, and how to use it correctly, even if you’ve never worked with databases before.

What Is Table Indexing in MySQL?

Simple Definition

A MySQL index is a data structure that improves the speed of data retrieval from a table.

Indexes work like a table of contents in a book.

Without Index

  • MySQL scans every row

  • Slower performance

With Index

  • MySQL finds data quickly

  • Much faster queries

Why Is Indexing Important?

  • Faster SELECT queries
  •  Improved search performance
  •  Efficient filtering (WHERE, JOIN, ORDER BY)
  • Better scalability for large tables

⚠️ Important:
Indexes speed up reading data, but they slightly slow down INSERT, UPDATE, DELETE operations.

Real-Life Analogy

Database ConceptReal-Life Example
TableBook
RowPage
ColumnTopic
IndexBook Index

👉 Without an index, you read every page.
👉 With an index, you jump directly to the page.

How Indexing Works in MySQL

  • MySQL creates a sorted structure

  • Stores column values with pointers to rows

  • Uses B-Tree (default) for most indexes

  • Searches become faster because MySQL avoids full table scans

Basic Index Syntax

Creating an Index

 
CREATE INDEX index_name ON table_name(column_name);

Example

CREATE INDEX idx_city
ON customers(city);

Speeds up searches on the city column.

Sample Table for Examples

Table: customers

idnamecityemail
1RahulDelhir@gmail.com
2NehaMumbain@gmail.com
3AmitDelhia@gmail.com

Example 1: Query Without Index

 
SELECT * FROM customers WHERE city = 'Delhi';

MySQL scans every row to find matching records.

Example 2: Query With Index

 
CREATE INDEX idx_city ON customers(city);
 
SELECT * FROM customers WHERE city = 'Delhi';

 MySQL uses the index to locate rows quickly.

Types of Indexes in MySQL

 PRIMARY KEY Index

  • Automatically created

  • Unique + Not NULL

  • One per table

 
PRIMARY KEY (id)

 UNIQUE Index

  • Prevents duplicate values

 
CREATE UNIQUE INDEX idx_email ON customers(email);

✔ No two customers can have the same email.

 NORMAL (NON-UNIQUE) Index

  • Most common

  • Allows duplicate values

 
CREATE INDEX idx_city ON customers(city);

COMPOSITE (MULTI-COLUMN) Index

  • Index on multiple columns

 
CREATE INDEX idx_city_name ON customers(city, name);

✔ Useful when filtering by both columns together

FULLTEXT Index

  • Used for text search

  • Works with MATCH() and AGAINST()

 
CREATE FULLTEXT INDEX idx_name ON customers(name);

 

When Should You Use Indexes?

  • Frequently searched columns
  •  Columns used in WHERE clause
  •  Columns used in JOIN
  •  Columns used in ORDER BY
  •  Large tables

When NOT to Use Indexes

  • Very small tables
  •  Columns with many updates
  •  Columns with low data variation (e.g., gender)

Indexing and WHERE Clause

 
SELECT * FROM customers
WHERE email = 'r@gmail.com';

✔ Index on email makes this query extremely fast.

Indexing and JOIN Performance

 
SELECT orders.id, customers.name
FROM orders
JOIN customers
ON orders.customer_id = customers.id;

✔ Indexes on customer_id and id improve JOIN speed.

Checking Existing Indexes

 
SHOW INDEX FROM customers;

✔ Displays all indexes on a table.

Removing an Index

 
DROP INDEX idx_city ON customers;

Common Beginner Mistakes

❌ Indexing Every Column

  • Too many indexes reduce performance

❌ Ignoring Composite Index Order

 
(city, name) ≠ (name, city)

❌ Forgetting Index Impact on INSERT/UPDATE

Indexes slow down write operations.

Best Practices for Table Indexing

  • Index only frequently searched columns
  •  Use composite indexes wisely
  •  Use EXPLAIN to analyze queries
  • Avoid unnecessary indexes
  •  Regularly review indexes

Using EXPLAIN to See Index Usage

EXPLAIN SELECT * FROM customers WHERE city = ‘Delhi’;
✔ Shows whether MySQL uses an index or not.

 

Quick Comparison: Indexed vs Non-Indexed Search

FeatureWithout IndexWith Index
SpeedSlowFast
Table ScanFull scanPartial
PerformanceLowHigh