How to do this problem properly in PL/SQL?

Question

Utilize the Outdoor Clubs & Product database to create a PL/SQL anonymous block program unit that lists the product_name attribute value and a demand status text display. The demand status text display is determined by counting the number of times a product has been ordered so far. The demand status text display will be either "Low Demand" or "High Demand". Low Demand is displayed if the product has been ordered less than 2 times. High Demand is displayed if the product has been ordered more than 2 times. Problem extension: Due to the business rule of not carrying products that have low demand, reduce the price of products (by $1) that have low demand.

I know my code is wrong considering it doesn't even run, but I am just stumped on this.

set serveroutput on clear screen declare product_name string; demand_status string; begin select product_name into product_name from product; select product_id into demand_status from order_details; dbms_output.put_line('Product name' || 'Demand status'); dbms_output.put_line('------------' || '--------------'); dbms_output.put_line(product_name || demand_status); end;

The results should look something like this:

Product Name             Demand Status
------------             -------------
Beginner's Ski Boot      Low Demand
Intermediate Ski Boot    High Demand
Pro Ski Boot             Low Demand
Beginner's Ski Pole      Low Demand
Intermediate Ski Pole    Low Demand
Pro Ski Pole             High Demand
Road Bicycle             Low Demand
Mountain Bicycle         Low Demand
Tire Pump                Low Demand
Water Bottle             High Demand
Bicycle Tires            Low Demand
Bicycle Helmet           Low Demand

Order_Details table Product table

Here is the code to the database tables:

drop table order_details;
drop table product_order;
drop table club_membership;
drop table purchase_order;
drop table product;
drop table customer;
drop table club_activity;
drop table sporting_clubs;
drop table supplier;

drop sequence club_sequence;
drop sequence product_id_sequence;
drop sequence customer_sequence;
drop sequence membership_sequence;
drop sequence product_order_sequence;
drop sequence supplier_sequence;
drop sequence po_sequence;

create table sporting_clubs
(club_id number(3)constraint sporting_clubs_pk primary key,
name varchar2(30),
street varchar2(30),
city varchar2(15),
state char(2),
zip number(5),
phone varchar2(10));

create table club_activity
(club_id number(3)constraint club_activity_fk references sporting_clubs,
activity varchar2(15),
constraint club_activity_pk primary key (club_id,activity));

create table supplier
(supplier_id varchar2(4) constraint supplier_pk primary key,
name varchar2(30),
street varchar2(30),
city varchar2(15),
state char(2),
zip number(5),
phone varchar2(10));

create table product
(product_id number(5) constraint product_pk primary key,
product_name varchar2(30),
quantity_in_stock number(3),
reorder_point number(2),
price number(5,2),
supplier_id varchar2(4) constraint product_fk references supplier,
reorder_qty number(2));

create table purchase_order
(po_no varchar2(4) constraint purchase_order_pk primary key,
po_date date,
product_id number(5) constraint purchase_order_fk1 references product,
quantity number(3),
supplier_id varchar2(4) constraint purchase_order_fk2 references supplier);

create table customer
(customer_id number(3) constraint customer_pk primary key,
first_name varchar2(10),
last_name varchar2(10),
street varchar2(30),
city varchar2(15),
state char(2)default 'MO',
zip number(5),
phone varchar2(10));

create table club_membership
(membership_id number(5) constraint club_membership_pk primary key,
membership_date date,
duration number(2),
amount number(4),
payment_type varchar2(5)constraint membership_payment_type_ck check ((payment_type = 'CC') or (payment_type = 'Check')),
club_id number(3) constraint club_membership_fk1 references sporting_clubs,
customer_id number(3) constraint club_membership_fk2 references customer);

create table product_order
(order_id number(4) constraint product_order_pk primary key,
order_date date,
ship_date date,
payment_type varchar2(5)constraint prod_order_payment_type_ck check ((payment_type = 'CC') or (payment_type = 'Check')),
total number (6,2),
customer_id number(3) constraint product_order_fk1 references customer);

create table order_details
(order_id number(4),
product_id number(5),
quantity number(2),
constraint order_details_pk primary key (order_id,product_id),
constraint order_details_fk1 foreign key (order_id) references product_order,
constraint order_details_fk2 foreign key (product_id) references product);


create sequence club_sequence
start with 100
increment by 10
nocache;

insert into sporting_clubs
values(club_sequence.nextval, 'Hillside Mountain Club', '1 Winona St','Wichita','KS',34342,'3163997676');
insert into sporting_clubs
values(club_sequence.nextval, 'Branson Climbing Club', '2 Sherwood Dr.','Branson','MO',65670,'4174485676');
insert into sporting_clubs
values(club_sequence.nextval, 'Cherokee Rafting Club', '44 Kent Ave.','St. Charles','MO',66572,'3147780870');
insert into sporting_clubs
values(club_sequence.nextval, 'White Plains Club', '225 Tracy St.','New York','NY',13567,'2126678090');

insert into club_activity
values(100,'Hiking');
insert into club_activity
values(100,'Climbing');
insert into club_activity
values(100,'Walking');
insert into club_activity
values(110,'Hiking');
insert into club_activity
values(110,'Climbing');
insert into club_activity
values(110,'Conservation');
insert into club_activity
values(110,'Walking');
insert into club_activity
values(120,'Conservation');
insert into club_activity
values(120,'Canoeing');
insert into club_activity
values(130,'Conservation');
insert into club_activity
values(130,'Canoeing');
insert into club_activity
values(130,'Walking');

create sequence supplier_sequence
start with 500
increment by 10
nocache;

insert into supplier
values('S'||supplier_sequence.nextval,'Hillside Ski','2717 S. Western Ave.','Los Angeles','CA',90006,'7146654959');
insert into supplier
values('S'||supplier_sequence.nextval,'Tiger Mountain','2600 S. Vermont Ave.','Los Angeles','CA',90006,'7143327878');
insert into supplier
values('S'||supplier_sequence.nextval,'Asha Outdoor','44 S. LaSalle St.','Chicago','IL',60603,'3125554678');
insert into supplier
values('S'||supplier_sequence.nextval,'Sheraton Recreation','225 Tracy St.','New York','NY',13567,'2128889569');


create sequence product_id_sequence
start with 10010
increment by 1
nocache;

insert into product
values(product_id_sequence.nextval,'Beginner''s Ski Boot',20,5,9.75,'S500',25);
insert into product
values(product_id_sequence.nextval,'Intermediate Ski Boot',18,5,12.99,'S500',20);
insert into product
values(product_id_sequence.nextval,'Pro Ski Boot',21,7,15.49,'S510',25);
insert into product
values(product_id_sequence.nextval,'Beginner''s Ski Pole',15,3,25.49,'S500',20);
insert into product
values(product_id_sequence.nextval,'Intermediate Ski Pole',20,3,29.99,'S520',22);
insert into product
values(product_id_sequence.nextval,'Pro Ski Pole',21,5,34.99,'S530',25);
insert into product
values(product_id_sequence.nextval,'Road Bicycle',15,4,34.95,'S520',18);
insert into product
values(product_id_sequence.nextval,'Mountain Bicycle',19,4,49.99,'S520',20);
insert into product
values(product_id_sequence.nextval,'Tire Pump',8,2,7.99,'S530',10);
insert into product
values(product_id_sequence.nextval,'Water Bottle',25,4,2.49,'S510',25);
insert into product
values(product_id_sequence.nextval,'Bicycle Tires',30,5,4.99,'S500',33);
insert into product
values(product_id_sequence.nextval,'Bicycle Helmet',23,6,10.95,'S510',25);

create sequence po_sequence
start with 11
nocache;

insert into purchase_order
values('PO'||po_sequence.nextval,to_date('5/25/12','mm/dd/yy'),10011,20,'S500');
insert into purchase_order
values('PO'||po_sequence.nextval,to_date('5/12/12','mm/dd/yy'),10015,25,'S530');
insert into purchase_order
values('PO'||po_sequence.nextval,to_date('6/25/12','mm/dd/yy'),10011,20,'S500');
insert into purchase_order
values('PO'||po_sequence.nextval,to_date('6/15/12','mm/dd/yy'),10018,10,'S530');
insert into purchase_order
values('PO'||po_sequence.nextval,to_date('7/10/12','mm/dd/yy'),10015,25,'S530');
insert into purchase_order
values('PO'||po_sequence.nextval,to_date('7/25/12','mm/dd/yy'),10019,25,'S510');


create sequence customer_sequence
start with 101
nocache;

insert into customer
values(customer_sequence.nextval,'Jack','Russell','25 North Madison Ave.','Springfield','MO',65807,'4178823434');
insert into customer
values(customer_sequence.nextval,'Betty','Trumbell','550 South Court Dr.','St. Louis','MO',63140,'3125556670');
insert into customer
values(customer_sequence.nextval,'Anil','Kaul','400 South Circle St.','Kansas City','MO',64530,'4316667070');
insert into customer
values(customer_sequence.nextval,'Tom','Wiley','1500 North Grand St.','Springfield','MO',65810,'4178825560');
insert into customer
values(customer_sequence.nextval,'Sharon','Stone','200 West Wagner St.','Springfield','MO',65807,'4176668890');

create sequence membership_sequence
start with 10010
increment by 10
nocache;

insert into club_membership
values(membership_sequence.nextval,to_date('6/12/12','mm/dd/yy'),4,200,'CC',100,101);
insert into club_membership
values(membership_sequence.nextval,to_date('6/15/12','mm/dd/yy'),2,100,'Check',110,102);
insert into club_membership
values(membership_sequence.nextval,to_date('6/21/12','mm/dd/yy'),5,250,'Check',120,103);

create sequence product_order_sequence
start with 1001
nocache;

insert into product_order
values(product_order_sequence.nextval,to_date('5/27/12','mm/dd/yy'),to_date('6/1/12','mm/dd/yy'),'CC',134.95,102);
insert into product_order
values(product_order_sequence.nextval,to_date('5/28/12','mm/dd/yy'),to_date('6/2/12','mm/dd/yy'),'CC',134.85,103);
insert into product_order
values(product_order_sequence.nextval,to_date('5/28/12','mm/dd/yy'),to_date('6/3/12','mm/dd/yy'),'Check',12.45,104);
insert into product_order
values(product_order_sequence.nextval,to_date('6/5/12','mm/dd/yy'),to_date('6/10/12','mm/dd/yy'),'CC',44.43,105);
insert into product_order
values(product_order_sequence.nextval,to_date('6/6/12','mm/dd/yy'),to_date('6/8/12','mm/dd/yy'),'Check',52.48,103);
insert into product_order
values(product_order_sequence.nextval,to_date('6/8/12','mm/dd/yy'),to_date('6/12/12','mm/dd/yy'),'CC',131.94,104);


insert into order_details values(1001,10011,2);
insert into order_details values(1001,10015,3);
insert into order_details values(1002,10011,5);
insert into order_details values(1002,10016,2);
insert into order_details values(1003,10019,5);
insert into order_details values(1004,10018,3);
insert into order_details values(1004,10011,1);
insert into order_details values(1004,10019,3);
insert into order_details values(1005,10017,1);
insert into order_details values(1005,10019,1);
insert into order_details values(1005,10021,1);
insert into order_details values(1006,10012,4);
insert into order_details values(1006,10015,2);

commit;

Answer 1

First, you have to calculate the number of orders per product. so you can join the two tables a Group the result by product.

select product_name
       ,count(1) as cnt_orders
from product p
join order_details o on p.product_id = o.product_id
group by p.product_name;

using a counter column you can get a value "Low Demand" or "High Demand". eg case when t.cnt_orders < 2 then 'Low' else 'High' end as "Demand status"

Finally, you iterate on the results and can print out the results. Here is a way you can do it. this doesn't cover the extended Problem, it just print a list like in your example.

BEGIN
  dbms_output.put_line(RPAD('Product name',28,' ') || 'Demand status');
  dbms_output.put_line('------------' || '--------------');
  for rec in (select t.product_name
                    ,case
                       when t.cnt_orders < 2 then
                        'Low'
                       else
                        'High'
                     end as DemandStatus              
                from (select product_name
                            ,count(1) as cnt_orders
                        from product p
                        left join order_details o on p.product_id = o.product_id
                       group by p.product_id
                               ,p.product_name
                       order by p.product_id) t)
  LOOP

    dbms_output.put_line(RPAD(rec.product_name,28,' ') || rec.DemandStatus);

  END LOOP;

END;
/

dbms_output:
Product name                Demand status
------------                --------------
Beginner's Ski Boot         Low
Intermediate Ski Boot       High
Pro Ski Boot                Low
Beginner's Ski Pole         Low
Intermediate Ski Pole       Low
Pro Ski Pole                High
Road Bicycle                Low
Mountain Bicycle            Low
Tire Pump                   Low
Water Bottle                High
Bicycle Tires               Low
Bicycle Helmet              Low
> 

db<>fiddle here

Answer 2

declare
cursor p_cur is
select product_id, product_name
from product;
p_row p_cur%rowtype;
product_count integer;
pname char(25);
begin
dbms_output.put_line('Product Name             Demand Status');
dbms_output.put_line('------------             -------------');
for p_row in p_cur
loop
select count(*) into product_count
from order_details
where product_id = p_row.product_id;
pname := p_row.product_name;
if product_count < 2 then
dbms_output.put_line(pname||'Low Demand');
update product
set price = price - 1
where product_id = p_row.product_id;
else
dbms_output.put_line(pname||'High Demand');
end if;
end loop;
end;