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Table of contents
Understanding Indexes
MUL Index in MySQL
Example of MUL Index
Importance of MUL Index
Frequently Asked Questions
What does MUL stand for in MySQL?
When should I use a MUL index?
Does a MUL index slow down write operations?
Last Updated: Mar 27, 2024

mul mean in mysql

Author Gunjan Batra
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Prerita Agarwal
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MySQL is a robust database management system that offers a broad range of tools and options to manage data efficiently. Among these options, MySQL uses indexing, a critical feature that helps speed up data retrieval. 

Mul mean in MYSQL

In this article, we'll look at one specific type of index represented by the keyword MUL - the Multiple Key Index.

Understanding Indexes

An index in MySQL is a data structure that improves the speed of data retrieval operations. Imagine having a book without an index or a table of contents. You would have to go through each page to find a specific topic. An index works the same way in a database; it helps to find data quickly without scanning the entire table.

MUL Index in MySQL

In MySQL, when you inspect a table structure using the SHOW COLUMNS or DESCRIBE command, you may notice that the "Key" column contains one of three values: PRI, UNI, or MUL. These represent different types of indexes.

The MUL in this list stands for 'Multiple'. It means that the field has a non-unique index, allowing multiple rows to have identical values in that column. This type of index is typically created when you implement a JOIN operation between two tables or when you want to ensure that certain queries run efficiently.

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Example of MUL Index

Let's take an example of two tables, Orders and Customers, linked by a column CustomerID. Here's how the tables look:


ID (PRI) Name
1 John
2 Alice
3 Bob
customers table


ID (PRI) Product CustomerID (MUL)
1 Apples 2
2 Bananas 3
3 Cherries 1
4 Blueberries 1
Orders table

In this case, the CustomerID in the Orders table would be a MUL index. It's non-unique (John has ordered twice) and it provides a link between the Orders and Customers tables.

Importance of MUL Index

The MUL index is crucial when you want to optimize your database performance. With the MUL index, MySQL can quickly locate the data without scanning the entire table, improving retrieval speed.

While beneficial, indexes (including MUL) should be used judiciously, as they come with their own cost. They can take up considerable disk space and slow down the performance of write queries (INSERT, UPDATE, DELETE), as indexes need to be updated each time the data changes.

Frequently Asked Questions

What does MUL stand for in MySQL?

In MySQL, MUL stands for 'Multiple', which indicates a non-unique index in the table.

When should I use a MUL index?

You should use a MUL index when you have non-unique fields that you often query and want to optimize retrieval speed.

Does a MUL index slow down write operations?

Yes, as with all indexes, a MUL index can slow down write operations as the index needs to be updated each time data changes.


Understanding MySQL's indexing system, including the MUL index, is crucial for designing and optimizing your databases. While the MUL index improves data retrieval speed, remember to use it judiciously due to its effect on write operations. 

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