public function where($field, $op, $value)
    {
        $this->pending['where'][] = array(
            'type'  => 'and',
            'field' => $field,
            'op'    => $op,
            'value' => $value,
        );

        return $this;
    }
public function where($field, $op, $value)
    {
        $this->pending['where'][] = array(
            'type'  => 'and',
            'field' => $field,
            'op'    => $op,
            'value' => $value,
        );

        return $this;
    }
public function where ( $ field , $ op , $ value ) { $ this -> pending [ 'where' ] [ ] = array ( 'type' => 'and' , 'field' => $ field , 'op' => $ op , 'value' => $ value , ) ; return $ this ; }
Where function, like SQL

Operators:
- Standard operators (=, !=, >, <, >=, <=)
- IN (only for array value)
- NOT IN (only for array value)

@param string $field Field name
@param string $op Operator
@param mixed $value Field value
@return self
Where function like SQL