Hey there, let's work through fixing that "access denied" error you're hitting with multiple database connections in CodeIgniter. I've tackled this exact issue a few times, so here's a step-by-step breakdown of what to check:

Let's start with the basics—your default DB config snippet looks like this:

$db['default'] = array(
    'hostname' => 'localhost',
    'username' => 'bd1',
    'password' => 'pass3214',
    'database' => 'db1',
    // ... other settings
);

• Verify that bd1 has the correct password (pass3214) for the db1 database. Typos here are the #1 culprit—even an extra space or capitalization mismatch will trigger an access denial.
• Test these credentials directly using a MySQL client (like phpMyAdmin, MySQL Workbench, or the command line):

  mysql -u bd1 -p pass3214 db1
  

If you can't connect here, the problem is with your MySQL user setup, not CodeIgniter.

MySQL ties users to specific hosts, and this is a super common gotcha:

• Your user bd1 might only be allowed to connect from localhost, but if your app is trying to use an IP (like 127.0.0.1) or a remote host, it'll get blocked.
• Run this query in your MySQL server to check allowed hosts for bd1:

  SELECT user, host FROM mysql.user WHERE user = 'bd1';
  

• If you don't see localhost or % (which allows connections from any host), grant the necessary permissions:

  GRANT ALL PRIVILEGES ON db1.* TO 'bd1'@'localhost' IDENTIFIED BY 'pass3214';
  FLUSH PRIVILEGES;
  

Since you mentioned multiple connections, make sure your second DB group is configured correctly:

• If you added a second group (e.g., $db['second_db']), double-check that it has its own unique credentials, hostname, and database name—don't just copy-paste the default and forget to update values.
• When loading the second connection in CodeIgniter, ensure you're specifying it properly to avoid overwriting the default:

  // Load the second connection as a separate object
  $this->second_db = $this->load->database('second_db', TRUE);
  

• If you're switching between connections, make sure you're referencing the correct object (e.g., $this->second_db->query(...) instead of $this->db->query(...)).

CodeIgniter uses environment settings that can override your default config:

• If ENVIRONMENT is set to production in index.php, db_debug is disabled, which hides the exact error message. Temporarily set db_debug to TRUE to get the full MySQL error—it'll tell you exactly why access is denied (wrong user, password, host, etc.).
• Look for environment-specific config files (like application/config/production/database.php)—these can overwrite your default settings without you realizing it.

• Make sure your MySQL server is running. On Linux, check with systemctl status mysql; on Windows, check the Services panel.
• Try swapping hostname from localhost to 127.0.0.1. Sometimes localhost uses a Unix socket that's misconfigured, while 127.0.0.1 uses TCP/IP which might work better.

Rare, but possible: local firewalls or antivirus software can block MySQL's default port (3306). Temporarily disable them to see if that fixes the issue.

内容的提问来源于stack exchange，提问作者Biswajit17