


What is the difference between utf8 and utf8mb4 character sets in MySQL?
Jun 18, 2025 am 12:11 AMMySQL's utf8 does not fully support UTF-8 encoding, while utf8mb4 supports it in full. Specifically, utf8 only supports up to 3 bytes of characters, and cannot correctly process 4-byte characters such as emojis, some rare Chinese characters and mathematical symbols, which may lead to data loss or errors; utf8mb4 supports all Unicode characters, accurately covering all symbols required for modern communications, and maintaining backward compatibility. Switching to utf8mb4 requires updating the character set of database, tables and columns, setting the connection character set, and repairing the converted data. In addition, you need to pay attention to whether the connection encoding, backup files and sorting rules match utf8mb4 to avoid potential problems.
If you're working with MySQL and dealing with character sets, especially for handling special characters like emojis or certain Asian scripts, you've probably come across the terms utf8
and utf8mb4
. But what's the real difference? Simply put: MySQL's utf8
doesn't fully support UTF-8 encoding , while utf8mb4
does. That might sound minor, but it has real-world consequences.
Let's break this down in a practical way.
Why MySQL's utf8
is not really UTF-8
In MySQL, the utf8
character set was originally designed to support Unicode, but with a major limitation: it only supports characters that take up to 3 bytes in UTF-8 encoding . True UTF-8, however, can use up to 4 bytes per character — and that's where the problem lies.
For example:
- Characters like é, ü, or Chinese (Chinese) are fine under
utf8
because they fit within 3 bytes. - But newer characters like emojis (?, ??), some rare Chinese characters, or mathematical symbols require 4 bytes and will be rejected or mangled if stored in a
utf8
column.
This means if your application accepts user-generated content (like social media posts, comments, etc.), using utf8
can lead to data loss or errors when users try to input these characters.
What utf8mb4
brings to the table
The utf8mb4
character set in MySQL is the proper implementation of full UTF-8 encoding. It:
- Supports all Unicode characters, including those that need 4 bytes.
- Handles modern communication needs like emojis, rare symbols, and more languages ??accurately.
- Is backward compatible with most of the characters supported by
utf8
.
Switching to utf8mb4
ensures your database can store any character from any language without issues. This makes it especially important for global applications or platforms where users may input text from various sources.
How to switch from utf8
to utf8mb4
Changing to utf8mb4
involves more than just altering a column or table. Here's what you typically need to do:
- Update your database, tables, and columns to use
utf8mb4
. - Set the default character set in your MySQL configuration (
my.cnf
ormy.ini
) toutf8mb4
. - Make sure your connection settings (like in PHP, Python, or other apps) also specify UTF-8 or
utf8mb4
as the connection charset. - Don't forget to rebuild indexes or repair tables after conversion, especially if you're converting large datasets.
Also, keep in mind that switching to utf8mb4
may slightly increase storage usage since some characters now take up more space. But for most modern applications, the trade-off is worth it.
Common pitfalls and how to avoid them
Even after switching to utf8mb4
, things can still go wrong if you miss one piece of the puzzle:
- Connection encoding not set : If your app connects using
utf8
, it won't send or retrieve 4-byte characters correctly. - Old backups or dumps : Restoring a backup made before switching to
utf8mb4
can reintroduce encoding issues. - Using
utf8
collations : Double-check that you're usingutf8mb4_unicode_ci
or similar, not the olderutf8_unicode_ci
.
Always test thoroughly after making changes — insert emojis, rare characters, and non-Latin scripts into your app to make sure everything saves and displays correctly.
That's the core of the difference between utf8
and utf8mb4
in MySQL. It's not a flashy topic, but it's cruel for handling modern data properly.
The above is the detailed content of What is the difference between utf8 and utf8mb4 character sets in MySQL?. For more information, please follow other related articles on the PHP Chinese website!

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