A Codigniter mysql driver that adds the ability to have "INSERT ... ON DUPLICATE UPDATE" statements. This is a forked version which has been changed to appear more inline with the built in Codeigniter functions.

MY_DB_mysql_driver.php

<?php  if (! defined('BASEPATH')) exit('No direct script access allowed');
 
class MY_DB_mysql_driver extends CI_DB_mysql_driver {
 
	final public function __construct($params) {
		parent::__construct($params);
	}
 
	/**
	 * Insert_On_Duplicate_Update
	 *
	 * Compiles insert strings and runs the queries
	 * MODIFIED to do a MySQL 'ON DUPLICATE KEY UPDATE'
	 *
	 * @access public
	 * @param string the table to retrieve the results from
	 * @param array an associative array of insert values
	 * @param bool whether or not to replace or add on update
	 * @return object
	 */
	function insert_on_duplicate_update($table = '', $set = NULL, $add = false)
	{
		if ( ! is_null($set))
		{
			$this->set($set);
		}
 
		if (count($this->ar_set) == 0)
		{
			if ($this->db_debug)
			{
				return $this->display_error('db_must_use_set');
			}
			return FALSE;
		}
 
		if ($table == '')
		{
			if ( ! isset($this->ar_from[0]))
			{
				if ($this->db_debug)
				{
					return $this->display_error('db_must_set_table');
				}
				return FALSE;
			}
 
			$table = $this->ar_from[0];
		}
 		
 		$sql = $this->_insert_on_duplicate_update($this->_protect_identifiers($table, TRUE, NULL, FALSE), array_keys($this->ar_set), array_values($this->ar_set), $add);
 
		$this->_reset_write();
		return $this->query($sql);
	}

	/**
	 * Insert_On_Duplicate_Update_Batch
	 *
	 * Compiles batch insert strings and runs the queries
	 * MODIFIED to do a MySQL 'ON DUPLICATE KEY UPDATE'
	 *
	 * @access public
	 * @param string the table to retrieve the results from
	 * @param array an associative array of insert values
	 * @param bool whether or not to replace or add on update
	 * @return object
	 */
	function insert_on_duplicate_update_batch($table = '', $set = NULL, $add = false)
	{
		if ( ! is_null($set))
		{
			$this->set($set);
		}
 
		if (count($this->ar_set) == 0)
		{
			if ($this->db_debug)
			{
				return $this->display_error('db_must_use_set');
			}
			return FALSE;
		}
 
		if ($table == '')
		{
			if ( ! isset($this->ar_from[0]))
			{
				if ($this->db_debug)
				{
					return $this->display_error('db_must_set_table');
				}
				return FALSE;
			}
 
			$table = $this->ar_from[0];
		}

		//get all column names from first index only
		foreach ($this->ar_set["`0`"] as $key => $val) {
			$keys[] =  $key;
		}

		//strip out the values from each item
		foreach ($this->ar_set as $item) {
			$itemVal = [];
			foreach ($item as $key => $val) {
				$itemVal[] = $val;
			}
			$values[] = $itemVal;
		}

 		$sql = $this->_insert_on_duplicate_update_batch($this->_protect_identifiers($table, TRUE, NULL, FALSE), $keys, $values, $add);
 
		$this->_reset_write();
		return $this->query($sql);
	}
 
	/**
	 * Insert_on_duplicate_update statement
	 *
	 * Generates a platform-specific insert string from the supplied data
	 * MODIFIED to include ON DUPLICATE UPDATE
	 *
	 * @access private
	 * @param string the table name
	 * @param array the insert keys
	 * @param array the insert values
	 * @param bool changes how values are updated
	 * @return string
	 */
	private function _insert_on_duplicate_update($table, $keys, $values, $add)
	{

		if ($add) {
			foreach($keys as $num => $key) {
				if (strpos($key, 'id') === false)
					$update_fields[] = $key .'='.$key.'+VALUES('. $key.')';
			}
		} else {
			foreach($keys as $num => $key) {
				$update_fields[] = $key .'='. $values[$num];
			}
		}
 
		$sql = "INSERT INTO ".$table." (".implode(', ', $keys).") VALUES (".implode(', ', $values).") ON DUPLICATE KEY UPDATE ".implode(', ', $update_fields);
		return $sql;
	}

	/**
	 * Insert_on_duplicate_update_batch statement
	 *
	 * Generates a platform-specific insert batch string from the supplied data
	 * MODIFIED to include ON DUPLICATE UPDATE
	 *
	 * @access private
	 * @param string the table name
	 * @param array the insert keys
	 * @param array the insert values
	 * @param bool changes how values are updated
	 * @return string
	 */
	private function _insert_on_duplicate_update_batch($table, $keys, $allValues, $add)
	{
		//create list of values within parenteses
		foreach ($allValues as $values) {
			$valueStr = '(';
			$valueStr .= implode(', ', $values);
			$valueStr .= ')';
			$theValues[] = $valueStr;
		}
 		
 		if ($add) {
 			foreach($keys as $num => $key) {
				if (strpos($key, 'id') === false)
					$update_fields[] = $key .'='.$key.'+VALUES('. $key.')';
			}
 		} else {
 			foreach($keys as $num => $key) {
				if (strpos($key, 'id') === false)
					$update_fields[] = $key .'='.$key.'VALUES('. $key.')';
			}
 		}

		$sql = "INSERT INTO ".$table." (".implode(', ', $keys).") ";
		$sql .= "VALUES ".implode(', ', $theValues)." ON DUPLICATE KEY UPDATE ".implode(', ', $update_fields);
		return $sql;
	}
}
?>

This extends the mysql driver which is deprecated and recommended to be using mysqli. There's a mysqli version on Github