orders.sql

--- for sqlfiddle go to http://sqlfiddle.com/#!17

create table customer(
  id serial primary key,
  name varchar(256)
  );
  
 create table ServiceOrder(
  id serial primary key,
  description varchar(256),
   customer_id INTEGER REFERENCES customer(id),
   timestamp TIMESTAMP
  );

 create table OrderLine(
   id serial primary key,
   part_number INTEGER,
   description varchar(256),
   quantity INTEGER,
   service_order INTEGER REFERENCES ServiceOrder(id)
  );


insert into customer (name) values ('Jim');
insert into customer (name) values ('Susan');
insert into customer (name) values ('John');
insert into customer (name) values ('Jaime');
insert into customer (name) values ('Sylvia');

insert into ServiceOrder (description, customer_id, timestamp) values ('widget order', 1, TO_TIMESTAMP('2019-01-01','YYYY-MM-DD'));
insert into ServiceOrder (description, customer_id, timestamp) values ('widget order', 2, TO_TIMESTAMP('2019-01-01','YYYY-MM-DD'));
insert into ServiceOrder (description, customer_id, timestamp) values ('widget order', 2, TO_TIMESTAMP('2019-01-02','YYYY-MM-DD'));
insert into ServiceOrder (description, customer_id, timestamp) values ('widget order', 2, TO_TIMESTAMP('2019-01-03','YYYY-MM-DD'));
insert into ServiceOrder (description, customer_id, timestamp) values ('widget order', 3, TO_TIMESTAMP('2019-01-01','YYYY-MM-DD'));
insert into ServiceOrder (description, customer_id, timestamp) values ('widget order', 4, TO_TIMESTAMP('2019-01-01','YYYY-MM-DD'));
insert into ServiceOrder (description, customer_id, timestamp) values ('widget order', 5, TO_TIMESTAMP('2019-01-01','YYYY-MM-DD'));

insert into OrderLine (part_number,description,quantity, service_order) values (123,'widget',45,1);
insert into OrderLine (part_number,description,quantity, service_order) values (123,'widget',1,2);
insert into OrderLine (part_number,description,quantity, service_order) values (123,'widget',5,3);
insert into OrderLine (part_number,description,quantity, service_order) values (123,'widget',2, 4);
insert into OrderLine (part_number,description,quantity, service_order) values (123,'widget',10, 5);
insert into OrderLine (part_number,description,quantity, service_order) values (123,'widget',11, 6);
insert into OrderLine (part_number,description,quantity, service_order) values (123,'widget',12,7);

--questions:
                                                                                                       
                                                                                                       --who ordered the most stuff?
SELECT c.name, sum(ol.quantity) as qty 
FROM customer c 
JOIN serviceorder so on c.id = so.customer_id 
JOIN orderline ol on so.id = ol.service_order
group by c.name order by qty;

--who placed the most orders ?
SELECT c.name, count(ol.quantity) as order_count 
FROM customer c 
JOIN serviceorder so on c.id = so.customer_id 
JOIN orderline ol on so.id = ol.service_order
group by c.name order by order_count;

--who ordered most recently?
SELECT c.name, so.timestamp as order_date 
FROM customer c 
JOIN serviceorder so on c.id = so.customer_id 
order by order_date;