public function getLeftColumns()
    {
        $columns = array();
        foreach ($this->left as $index => $column) {
            $columns[] = $this->getLeftColumn($index);
        }

        return $columns;
    }
public function getLeftColumns()
    {
        $columns = array();
        foreach ($this->left as $index => $column) {
            $columns[] = $this->getLeftColumn($index);
        }

        return $columns;
    }
public function getLeftColumns ( ) { $ columns = array ( ) ; foreach ( $ this -> left as $ index => $ column ) { $ columns [ ] = $ this -> getLeftColumn ( $ index ) ; } return $ columns ; }
Get the list of all the names of left columns of the join condition

@return array
Get the list of all the names of left columns of the join condition