Recover last error on database

Hi All,

please, I am trying recover the error message from a trigger in a database that is returned, but
must be honest, I don't know how I do!.

I have next code:

$result=$this->db->insert('vendedor',$datos);
if ($result==true){
return true;
}
else{
echo "Se produjo un error";
}

But I need the message from database for show it to the client.
I appreciate any help.
Best Regards.