MySQL charset=utf8mb4

Also Known As

TL;DR

Explanation

MySQL's 'utf8' charset is a 3-byte encoding that cannot store 4-byte Unicode code points (emoji, some CJK characters, mathematical symbols). 'utf8mb4' is the correct implementation of UTF-8 and supports the full Unicode range. Using 'utf8' causes silent data truncation or errors when 4-byte characters are inserted. The DSN should specify charset=utf8mb4 and the column/table/database collation should be utf8mb4_unicode_ci or utf8mb4_0900_ai_ci (MySQL 8+).

Watch Out

Common Misconception

Why It Matters

Common Mistakes

• Specifying charset=utf8 in the DSN — silent truncation of emoji and supplementary characters.
• Mixing utf8 and utf8mb4 columns in the same table — comparison and join operations may have unexpected collation errors.
• Forgetting to set utf8mb4 at the connection level even when the table columns are utf8mb4.

Avoid When

• Do not use utf8 — it silently truncates or errors on emoji and supplementary Unicode characters.

When To Use

• Always use utf8mb4 for any table that may store user-generated content, names, or multilingual text.
• Set charset=utf8mb4 in the DSN — not via SET NAMES — to ensure it applies at the protocol level.

Code Examples

// Wrong: utf8 truncates emoji silently
$pdo = new PDO('mysql:host=localhost;dbname=app;charset=utf8', $user, $pass);
// INSERT 'Hello 😀' → stored as 'Hello ' (emoji silently dropped)

// Correct: utf8mb4 in DSN and SET NAMES
$pdo = new PDO('mysql:host=localhost;dbname=app;charset=utf8mb4', $user, $pass);

-- SQL: table with correct charset
CREATE TABLE posts (
    id   INT AUTO_INCREMENT PRIMARY KEY,
    body TEXT
) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;

References

• ↗ https://dev.mysql.com/doc/refman/8.0/en/charset-unicode-utf8mb4.html

Tags

Related Terms