The linearity of filter                     

Introduction LOF
Filter linearity denotes the relationship between objects, operators and brackets. The position of brackets has direct impact on the result of our WHERE expression. We have already used expressions with brackets in the previous cases, for example:

SELECT ;
                                    order. number_invoice ;
                                    order. order_date ;
                                    order.value_invoice ;
                                    order. payment ;
                                    customer. company_ name ;
                        FROM order, customer ;
                         WHERE  ;
                                      order.order_id   IN (“   200”,”   300”,”   660”,”  1020” )

The feature of IN operator is to have brackets, in the same way as the extended objects. However, on the global level, the reflexive problem
 which is to be solved, can be very complicated and may imply the existence of brackets. Some reflections on linearity will facilitate the resolvement of some very difficult problem.
We shall take into consideration the following cases of filter linearity:
            1)       Linear filter
            2)       Quasi linear filter
            3)       NonLinear filter

Linear filter                                
We here consider the filtering expression without brackets with the AND/OR operator. We do not here include either the IN or extended object.
For example:

SELECT * ;
                        FROM order ;
                        WHERE ;
                                        BETWEEN(order_date ,23/05/1995 , 28/06/1995) .AND. ;
                                        BETWEEN(order.value_invoice , 2000,4000)

            or

SELECT * ;
                        FROM order ;
                        WHERE ;
                                        BETWEEN(order_date ,23/05/1995 , 28/06/1995) .OR. ;
                                        BETWEEN(order.value_invoice , 2000,4000)

That thing which is of our frequent interest, is when the filtering expression gets combined with the AND operator and that type of filter will be called the eliminating filter.

Quasi linear filter                            
If you use IN operator in the filtering expression, as well as the extended objects and advanced extended objects combined with OR/AND operator, you will get a quasi linear filter.

SELECT ;
                                    order. number_invoice ;
                                    order. order_date ;
                                    order.value_invoice ;
                                    order. payment ;
                                    customer. company_ name ;
                        FROM order, customer ;
                         WHERE  ;
                                      order.order_id   IN (“   200”,”   300”,”   660”,”  1020” ) .AND. ;
                                      order_date  >= 23/05/1995  .AND. ;
                                     (   BETWEEN(order.value_invoice ,200,220) .OR.;    
                                        BETWEEN(order.value_invoice ,300,330)      .OR. ;
                                        BETWEEN( order.value_invoice , 660,662)     .OR. ;
                                        BETWEEN(order.value_invoice ,1020,1270)  .OR. ;
                                        order.value_invoice => 1900)   )

 In essence, IN operator, extended object and advanced objects have brackets.