SQL Developer QUERY For uni assignment - sql

Question

I am stuck with the following queries. Anyone can help?
Show the full name and the phone number of the customer who made the most orders.
Which item is the best seller? Display description and price.
Attached is my ERD.
create table statements are as follows:
CREATE TABLE ITEMS (
itemID number(5),
itemDescription varchar2(60),
itemSize varchar2(22),
itemColour varchar2(10),
itemPrice number (5,2),
itemQuantityAvailable number(3),
CONSTRAINT pk_items PRIMARY KEY (itemID));
CREATE TABLE CUSTOMERS (
custID number(5),
custLName varchar2(10),
custFName varchar2(20),
custAddress varchar2(30),
custTown varchar2(20),
custPostcode number(4),
custPhone number(10),
custEmail varchar2(30),
shopID number(5),
CONSTRAINT pk_customers PRIMARY KEY (custID),
CONSTRAINT fk_customers_shopID FOREIGN KEY (shopID)
REFERENCES SHOPS (shopID));
CREATE TABLE ORDERS (
orderNo number(5),
orderDate Date,
dispatchDate date,
custID number(5),
CONSTRAINT pk_orders PRIMARY KEY (orderNo),
CONSTRAINT fk_orders_custID FOREIGN KEY (custID)
REFERENCES CUSTOMERS (custID));
CREATE TABLE OrderQuantity (
orderNo number(5),
itemID number(5),
orderQuantity number(3),
CONSTRAINT pk_orderQty PRIMARY KEY (itemID, orderNo),
CONSTRAINT fk_orderQty_itemID FOREIGN KEY (itemID)
REFERENCES ITEMS (itemID),
CONSTRAINT fk_orderQty_orderNo FOREIGN KEY (orderNO)
REFERENCES ORDERS (orderNo));
INSERT STATEMENTS ARE AS FOLLOWS:
INSERT INTO ITEMS VALUES (1,'ADIDAS MEN''S ID STADIUM FULL-ZIP JACKET','S/M/L/XL','Silver',89.99,100);
INSERT INTO ITEMS VALUES (2,'ADIDAS MEN''S ESSENTIALS 3 STRIPES CREW FRENCH TERRY','S/L/XL','Black',71.99,90);
INSERT INTO ITEMS VALUES (3,'ADIDAS MEN''s ESSENTIALS 3-STRIPES FLEECE PANT','M/L/XL/XXL','White',62.99,80);
INSERT INTO ITEMS VALUES (4,'NIKE MEN''S FULL-ZIP SPORTSWEAR HOODIE','M/L/XL','DarkGrey',67.49,70);
INSERT INTO ITEMS VALUES (5,'NIKE MEN''S HBR FLEECE CREW','S/L/XL','DarkGrey',58.49,60);
INSERT INTO ITEMS VALUES (6,'PUMA MEN''S ESSENTIAL SWEAT PANTS','XS/S/M/L/XL','Navy',45.00,50);
INSERT INTO ITEMS VALUES (7,'ADIDAS MEN''S ESSENTIALS CHELSEA SHORTS','M/L/XL','Green',35.99,40);
INSERT INTO ITEMS VALUES (8,'PUMA MEN''S CORE 7IN RUNNING SHORTS','S/L/XL','Black',26.99,20);
INSERT INTO ITEMS VALUES (9,'ASICS GT 2000 6 MEN''S RUNNING SHOES','8/8.5/9/9.5/10','Silver',239.00,90);
INSERT INTO ITEMS VALUES (10,'ASICS GEL-KAYANO 25 2E WIDE MEN''S RUNNING SHOE','9/9.5/10/10.5/11','Black',219.00,60);
INSERT INTO ITEMS VALUES (11,'REEBOK RUNNER 3.0 MEN''S RUNNING SHOES','8/8.5/10/10.5','Orange',209.00,10);
INSERT INTO ITEMS VALUES (12,'REEBOK MEN''S WORKOUT READY 2.0 TEE','XS/S/M','White',199.00,50);
INSERT INTO ITEMS VALUES (13,'UNDER ARMOUR RAPID MEN''S RUNNING SHOES','8.5/10/11','Black',199.00,20);
INSERT INTO ITEMS VALUES (14,'UNDER ARMOUR CHARGED MEN''S RUNNING SHOES','8/8.5/9/9.5/10','Silver',159.00,80);
INSERT INTO ITEMS VALUES (15,'ADIDAS SOLAR DRIVE MEN''S RUNNING SHOE','8/8.5/10/10.5','Black',139.00,30);
INSERT INTO CUSTOMERS VALUES (1,'Widimer','Cindy','121 King St','Box Hill',3195,0470121566,'cindy_widimer#gmail.com',1);
INSERT INTO CUSTOMERS VALUES (2,'Bohrman','Robert','54 Queens St','Murrumbeena',3195,0455131565,'robert_bohram#gmail.com',3);
INSERT INTO CUSTOMERS VALUES (3,'Clarke','Brenda','89 Pecket St','Oakleigh',3195,0424456123,'brenda.clarke#gmail.com',2);
INSERT INTO CUSTOMERS VALUES (4,'Cartier','Bruce','12 Parkore St','Mulgrave',3195,0425654123,'bruce.cartier#gmail.com',3);
INSERT INTO CUSTOMERS VALUES (5,'Heart','Lucy','45 Rose St','Hampton Park',3178,0470456321,'lucy.heart#gmail.com',1);
INSERT INTO CUSTOMERS VALUES (6,'Carter','Joan','123 Davdison St','Hampton Park',3178,0452123789,'carter_joangmail.com',3);
INSERT INTO CUSTOMERS VALUES (7,'John','Ailene','56 Spring St','Yaraman',3178,0475123159,'john.ailene#gmail.com',1);
INSERT INTO CUSTOMERS VALUES (8,'Lewis','Carl','45 Brendon Ct','Noble Park',3178,0454789456,'carl_lewis#gmail.com',3);
INSERT INTO CUSTOMERS VALUES (9,'Holden','Hilary','56 Swanston St','Sunshine',3020,0421456123,'hilar_holdengmail.com',1);
INSERT INTO CUSTOMERS VALUES (10,'Powell','Venus','124 Russel St','Richmond',3112,0431456753,'venus_powellgmail.com',2);
INSERT INTO CUSTOMERS VALUES (11,'Juliet','Susan','87 Fawkner Ct','South Yara',3141,0424687423,'susan_juliet#gmail.com',2);
INSERT INTO CUSTOMERS VALUES (12,'Price','Victor','125 William St','Flagstaff',3003,0465789123,'victor_price#gmail.com',2);
INSERT INTO ORDERS VALUES (1,'01/Jan/18','03/Feb/18',1);
INSERT INTO ORDERS VALUES (2,'20/Jan/18','05/Feb/18',3);
INSERT INTO ORDERS VALUES (3,'05/Feb/18','10/Feb/18',4);
INSERT INTO ORDERS VALUES (4,'18/Feb/18','22/Feb/18',5);
INSERT INTO ORDERS VALUES (5,'01/Mar/18','10/Mar/18',10);
INSERT INTO ORDERS VALUES (6,'12/Mar/18','15/Mar/18',12);
INSERT INTO ORDERS VALUES (7,'07/Apr/18','14/Apr/18',11);
INSERT INTO ORDERS VALUES (8,'25/Apr/18','27/Apr/18',3);
INSERT INTO ORDERS VALUES (9,'06/May/18','10/May/18',2);
INSERT INTO ORDERS VALUES (10,'17/Jun/18','20/Jun/18',5);
INSERT INTO ORDERS VALUES (11,'29/Jun/18','07/Jul/18',4);
INSERT INTO ORDERS VALUES (12,'08/Jul/18','14/Jul/18',11);
INSERT INTO ORDERS VALUES (13,'25/Jul/18','29/Jul/18',12);
INSERT INTO ORDERS VALUES (14,'01/Aug/18','18/Aug/18',5);
INSERT INTO ORDERS VALUES (15,'19/Aug/18','10/Sep/18',1);
INSERT INTO ORDERS VALUES (16,'11/Sep/18','15/Sep/18',4);
INSERT INTO ORDERS VALUES (17,'21/Sep/18','29/Sep/18',5);
INSERT INTO ORDERS VALUES (18,'01/Oct/18',null,10);
INSERT INTO ORDERS VALUES (19,'20/Oct/18',null,3);
INSERT INTO ORDERS VALUES (20,'23/Oct/18',null,1);
INSERT INTO OrderQuantity VALUES (1,1,20);
INSERT INTO OrderQuantity VALUES (2,3,10);
INSERT INTO OrderQuantity VALUES (3,4,20);
INSERT INTO OrderQuantity VALUES (4,5,14);
INSERT INTO OrderQuantity VALUES (5,10,10);
INSERT INTO OrderQuantity VALUES (6,11,15);
INSERT INTO OrderQuantity VALUES (7,12,10);
INSERT INTO OrderQuantity VALUES (8,3,25);
INSERT INTO OrderQuantity VALUES (9,2,50);
INSERT INTO OrderQuantity VALUES (10,5,20);
INSERT INTO OrderQuantity VALUES (11,4,10);
INSERT INTO OrderQuantity VALUES (12,11,20);
INSERT INTO OrderQuantity VALUES (13,12,10);
INSERT INTO OrderQuantity VALUES (14,5,10);
INSERT INTO OrderQuantity VALUES (15,1,10);
INSERT INTO OrderQuantity VALUES (16,4,30);
INSERT INTO OrderQuantity VALUES (17,5,9);
INSERT INTO OrderQuantity VALUES (18,10,30);
INSERT INTO OrderQuantity VALUES (19,3,20);
INSERT INTO OrderQuantity VALUES (20,1,15);

Answer 1

This is a simple example of how to solve it by making a subquery and only select the first row from it.
SELECT full_name, custPhone
FROM (SELECT CONCAT(custFName, ' ', custLName) as full_name, custPhone, COUNT(o.orderNo) num_orders
FROM ORDERS o
JOIN Customers c ON c.custId = o.custid
GROUP BY full_name, custPhone
ORDER BY num_orders Desc ) AS subq
WHERE ROWNUM = 1
and the same for the second query
SELECT itemDescription, itemPrice
FROM (SELECT itemDescription, itemPrice, SUM(orderQuantity) sum_quantity
FROM OrderQuantity o
JOIN Items i ON i.itemId = o.itemId
GROUP BY itemDescription, itemPrice
ORDER BY sum_quantity DESC) AS subq
WHERE ROWNUM = 1

Answer 2

check this sqlfiddle http://sqlfiddle.com/#!5/553399/39/0
The Full name and the phone number of the customers who made the most orders :
SELECT ORDERS.custID,CUSTOMERS.custFName,CUSTOMERS.custPhone,COUNT(ORDERS.orderNo )
FROM ORDERS inner join CUSTOMERS
on CUSTOMERS.custID =ORDERS.custID
group by ORDERS.custID,CUSTOMERS.custFName,CUSTOMERS.custPhone
order by COUNT(ORDERS.orderNo ) desc
Description and price of Bestseller Item (qty bestseller):
SELECT OrderQuantity.itemID ,ITEMS.itemDescription,ITEMS.itemPrice ,sum(distinct OrderQuantity.itemID )
FROM OrderQuantity inner join ITEMS
on OrderQuantity.itemID =ITEMS.itemID
GROUP BY OrderQuantity.itemID ,ITEMS.itemDescription,ITEMS.itemPrice
ORDER BY sum(distinct OrderQuantity.itemID) DESC
if you need only top bestseller item you can add rownum 1 to these queries.
select * from (SELECT OrderQuantity.itemID ,ITEMS.itemDescription,ITEMS.itemPrice ,sum(distinct OrderQuantity.itemID )
FROM OrderQuantity inner join ITEMS
on OrderQuantity.itemID =ITEMS.itemID
GROUP BY OrderQuantity.itemID ,ITEMS.itemDescription,ITEMS.itemPrice
ORDER BY sum(distinct OrderQuantity.itemID) DESC) q
Where rownum=1