CodeIgniter - how to catch DB errors?

Maybe this:

$db_debug = $this->db->db_debug; //save setting

$this->db->db_debug = FALSE; //disable debugging for queries

$result = $this->db->query($sql); //run query

//check for errors, etc

$this->db->db_debug = $db_debug; //restore setting

Use error() method:

$this->db->error(); 

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For CodeIgniter 2, you can use the following functions which are now deprecated:

$this->db->_error_message(); (mysql_error equivalent)
$this->db->_error_number(); (mysql_errno equivalent)