The DB_COLLATE constant in WordPress is used to define the collation of your database tables. Collation determines how string comparison is performed in the database, including the sort order and case sensitivity.

What Is Collation in Databases?

  • Collation is a set of rules that determines how strings are compared and sorted in a database.
  • It works in combination with the character set (DB_CHARSET), which defines the encoding of text in the database.

Common Collations in MySQL

Collation Description
utf8_general_ci Case-insensitive collation for UTF-8.
utf8_unicode_ci Case-insensitive, better for multilingual data.
utf8mb4_general_ci Case-insensitive collation for UTF-8 with full Unicode support (including emojis).
utf8mb4_unicode_ci Case-insensitive, better accuracy for multilingual data with full Unicode support.
utf8_bin Case-sensitive collation for UTF-8.

The Role of DB_COLLATE in WordPress

The DB_COLLATE constant defines the collation for WordPress database tables. If left empty, the default collation of the MySQL server is used.

Location in wp-config.php

define('DB_COLLATE', '');
  • Default value: An empty string ('') means WordPress will use the MySQL server default collation.
  • Custom value: You can set a specific collation, like:
define('DB_COLLATE', 'utf8mb4_unicode_ci');

Why Set or Change DB_COLLATE?

  1. To Ensure Consistency:
    • All tables in your database should ideally use the same collation to avoid errors like:
      • Illegal mix of collations
  2. For Full Unicode Support:
    • Use utf8mb4_unicode_ci to handle emojis and other special characters.
  3. Performance vs. Accuracy:
    • _general_ci: Faster, but less accurate for multilingual sorting.
    • _unicode_ci: More accurate for complex languages but slightly slower.

How to Check Your Current Collation

  1. In phpMyAdmin:
    • Go to your database.
    • Check the collation for each table under the "Collation" column.
  2. Using MySQL Command Line:
SELECT TABLE_NAME, TABLE_COLLATION
FROM INFORMATION_SCHEMA.TABLES
WHERE TABLE_SCHEMA = 'your_database_name';

How to Change Collation

1

Update the wp-config.php File

Change or add the DB_COLLATE constant:

define('DB_COLLATE', 'utf8mb4_unicode_ci');
2

Change Collation of Existing Tables

  1. Backup your database before making changes.
  2. Use a MySQL query to update collation for all tables:
ALTER TABLE wp_posts CONVERT TO CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;

Replace wp_posts with the table name.

3

Use a Plugin

Plugins like Better Search Replace can help update collation for all tables.

Best Practices

  1. Use utf8mb4 for Modern WordPress Sites:
    • utf8mb4_unicode_ci is recommended for full Unicode support, including emojis.
    • Avoid utf8, as it does not support the full range of Unicode characters.
  2. Ensure Compatibility:
    • Make sure your MySQL version supports the chosen collation (e.g., utf8mb4 requires MySQL 5.5.3 or later).
  3. Keep Collation Consistent:
    • All tables and columns should use the same collation to prevent conflicts.

Example: Setting DB_COLLATE in wp-config.php

define('DB_CHARSET', 'utf8mb4');
define('DB_COLLATE', 'utf8mb4_unicode_ci');
  • DB_COLLATE determines how text data is compared and sorted in WordPress.
  • Use utf8mb4_unicode_ci for modern WordPress installations.
  • Update collation consistently across the database to avoid errors.