WordPress requires a MySQL or MariaDB database. These constants configure the database connection.

Required Constants

DB_NAME

define( 'DB_NAME', 'wordpress' );

• Required: Yes
• Type: String
• Purpose: Name of the database WordPress will use
• Notes: Database must exist before WordPress installation

DB_USER

define( 'DB_USER', 'db_username' );

• Required: Yes
• Type: String
• Purpose: MySQL username with access to the database
• Security: Create a dedicated user for WordPress; never use root in production

DB_PASSWORD

define( 'DB_PASSWORD', 'secure_password_here' );

• Required: Yes
• Type: String
• Purpose: Password for the database user
• Security: Use strong, unique passwords; consider environment variables for sensitive data

DB_HOST

define( 'DB_HOST', 'localhost' );

• Required: Yes
• Type: String
• Default: localhost
• Purpose: MySQL server hostname or IP address

Common Values

Port and Socket Examples

// Custom port
define( 'DB_HOST', 'localhost:3307' );

// Unix socket (common on Linux)
define( 'DB_HOST', 'localhost:/var/run/mysqld/mysqld.sock' );

// Remote host with port
define( 'DB_HOST', 'db.example.com:3306' );

Character Set Constants

DB_CHARSET

define( 'DB_CHARSET', 'utf8mb4' );

• Required: No (but recommended)
• Type: String
• Default: utf8mb4 (since WordPress 4.2)
• Purpose: Database character set for storing content
• Recommendation: Always use utf8mb4 for full Unicode support (including emoji)

Common Values

DB_COLLATE

define( 'DB_COLLATE', '' );

• Required: No
• Type: String
• Default: Empty string (MySQL default for charset)
• Purpose: Database collation for sorting and comparison

Common Values

Note: Leave empty unless you have specific requirements. WordPress handles this automatically.

Advanced Database Constants

WP_ALLOW_REPAIR

define( 'WP_ALLOW_REPAIR', true );

• Type: Boolean
• Default: Not defined (false)
• Purpose: Enables the database repair page at /wp-admin/maint/repair.php
• Security: Only enable temporarily when needed; remove after repair

Important: This page is accessible without authentication! Always remove or set to false after use.

CUSTOM_USER_TABLE

define( 'CUSTOM_USER_TABLE', 'shared_users' );

• Type: String
• Purpose: Use a custom users table (for sharing users across installations)
• Use Case: Multiple WordPress installations sharing user accounts

CUSTOM_USER_META_TABLE

define( 'CUSTOM_USER_META_TABLE', 'shared_usermeta' );

• Type: String
• Purpose: Use a custom user meta table
• Note: Usually used together with CUSTOM_USER_TABLE

Database Connection Examples

Standard Local Setup

define( 'DB_NAME', 'wordpress' );
define( 'DB_USER', 'wp_user' );
define( 'DB_PASSWORD', 'strong_password' );
define( 'DB_HOST', 'localhost' );
define( 'DB_CHARSET', 'utf8mb4' );
define( 'DB_COLLATE', '' );

Remote Database

define( 'DB_NAME', 'wordpress_prod' );
define( 'DB_USER', 'wp_remote' );
define( 'DB_PASSWORD', 'very_strong_password' );
define( 'DB_HOST', 'db.example.com:3306' );
define( 'DB_CHARSET', 'utf8mb4' );
define( 'DB_COLLATE', '' );

Using Environment Variables

define( 'DB_NAME', getenv( 'WORDPRESS_DB_NAME' ) ?: 'wordpress' );
define( 'DB_USER', getenv( 'WORDPRESS_DB_USER' ) ?: 'root' );
define( 'DB_PASSWORD', getenv( 'WORDPRESS_DB_PASSWORD' ) ?: '' );
define( 'DB_HOST', getenv( 'WORDPRESS_DB_HOST' ) ?: 'localhost' );
define( 'DB_CHARSET', 'utf8mb4' );
define( 'DB_COLLATE', '' );

Socket Connection (Unix/Linux)

define( 'DB_HOST', 'localhost:/var/lib/mysql/mysql.sock' );
// or
define( 'DB_HOST', 'localhost:/tmp/mysql.sock' );

Shared User Tables Across Sites

For sharing users between multiple WordPress installations:

// Site A - Primary (creates the tables)
$table_prefix = 'site_a_';

// Site B - Uses Site A's user tables
$table_prefix = 'site_b_';
define( 'CUSTOM_USER_TABLE', 'site_a_users' );
define( 'CUSTOM_USER_META_TABLE', 'site_a_usermeta' );

Considerations:

• User roles/capabilities are stored in usermeta with table-prefix-specific keys
• Each site may need to add its own capability keys
• Plugins may not fully support this configuration

Troubleshooting

Error: "Error establishing a database connection"

1. Verify DB_NAME, DB_USER, DB_PASSWORD are correct
2. Check DB_HOST (try 127.0.0.1 instead of localhost)
3. Ensure MySQL/MariaDB service is running
4. Confirm user has privileges on the database

Test Database Connection

<?php
// test-db.php (delete after testing!)
$conn = new mysqli( 'localhost', 'db_user', 'db_pass', 'db_name' );
if ( $conn->connect_error ) {
    die( 'Connection failed: ' . $conn->connect_error );
}
echo 'Connected successfully';
$conn->close();

Grant Permissions (MySQL)

-- Create database
CREATE DATABASE wordpress CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_520_ci;

-- Create user and grant privileges
CREATE USER 'wp_user'@'localhost' IDENTIFIED BY 'strong_password';
GRANT ALL PRIVILEGES ON wordpress.* TO 'wp_user'@'localhost';
FLUSH PRIVILEGES;

Security Best Practices

1. Unique database name: Don’t use wordpress or predictable names
2. Dedicated user: Never use MySQL root account
3. Strong password: Use generated passwords (32+ characters)
4. Minimal privileges: Grant only necessary permissions
5. Local connections: Use localhost when possible; restrict remote access
6. Environment variables: Store credentials in environment, not in files committed to version control