Join tables                                

Introduction    JT                                      
So far we have been considering the problems with one table. Let’s study our problem in the situation when we have more tables to be joined, discussing, as well how to utilize Vdf objects.

For problem treating, we shall look at tables having the following fields:

                Table name : "order"

                 Table name : "customer"

While writing SQL commands, we shall not take into consideration any special conditions for the formation of “Select” expressions; we believe the user to be having sufficient knowledge of SQL
‘Where’ condition parts                                       
The user wants to extract all the facts and he will write the following SQL expression:

            SELECT ;
                        order. number_invoice ;
                        order. order_date ;
                        order.value_invoice ;
                        order. payment ;
                        customer. company_ name ;
                 FROM order, customer ;
                 WHERE ;
                          order.customer_id = customer.customer_id

             cxWhereCond = “order.customer_id = customer.customer_id” is the result of joining two tables into one query.

We should proceed. If the user wants to extract all the fact with the fact dates bigger than 23/05/1995, he will write the following SQL expression:  

            SELECT ;
                        order. number_invoice ;
                        order. order_date ;
                        order.value_invoice ;
                        order. payment ;
                        customer. company_ name ;
                 FROM order, customer ;
                 WHERE ;
                          order.customer_id = customer.customer_id  .AND.  ;
                          order_date >= 23/05/1995

             cxWhereCond = “order.customer_id = customer.customer_id  “ + “.AND. ”  
                                                            + ;
                                                “order_date >= 23/05/1995”