sql is not compiled properly

another error I found.

sending in this code results in

PHP Code:

$this->db->select_sum('amount * quantity', 'amount'); 


results as

Code:

SUM(`amount *` `quantity`) AS `amount`

the code responsible for the false quotes is

PHP Code:

public function protect_identifiers($item, $prefix_single = FALSE, $protect_identifiers = NULL, $field_exists = TRUE)
.......
 elseif ($offset = strrpos($item, ' '))
 {
 $alias = ($protect_identifiers)
 ? ' '.$this->escape_identifiers(substr($item, $offset + 1))
 : substr($item, $offset);
 $item = substr($item, 0, $offset);
 } 


another issue I found that

PHP Code:

public function select_sum($select = '', $alias = '') 


and

PHP Code:

protected function _max_min_avg_sum($select = '', $alias = '', $type = 'MAX') 


do not take protect_identifiers as a parameter like many other db functions do but just use the global

$this->_protect_identifiers

Honestly the database layer is need of a general overhaul. I have been looking into this only for 30 minutes and found 3 errors.
In general I must say that the database layer is inconsistent and badly programmed.