exception.php

См. документацию.

<?php
namespace Bitrix\Main\DB;

class Exception extends \Bitrix\Main\SystemException
{
    protected $databaseMessage;

    public function __construct($message = "", $databaseMessage = "", \Throwable $previous = null)
    {
        if (($message != "") && ($databaseMessage != ""))
            $message .= ": ".$databaseMessage;
        elseif (($message == "") && ($databaseMessage != ""))
            $message = $databaseMessage;
 
        $this->databaseMessage = $databaseMessage;
 
        parent::__construct($message, 400, '', 0, $previous);
    }

    public function getDatabaseMessage()
    {
        return $this->databaseMessage;
    }
}