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DB week_1 homework #27

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7e639e8
DB week_1 homework
Sep 24, 2020
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last answer corrected
Sep 24, 2020
a60fc0b
BD WEEK_2 HOMEWORK
Sep 25, 2020
faf6c09
week DB
Oct 26, 2020
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15 changes: 12 additions & 3 deletions week-1/mandatory/2-classes-db/task.md
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Expand Up @@ -7,9 +7,18 @@ Below you will find a set of tasks for you to complete to consolidate and extend
To submit this homework write the correct commands for each question here:

```sql


```
1- select * from rooms where rate >100;
2-select * from reservations where checkin_date between '2020-09-01' and '2020-09-30' and checkout_date - checkin_date >3;
3-select * from customers where city like 'M%';
4-insert into room_types( room_type, def_rate) values ('PENTHOUSE', 185.00);
5-insert into rooms( room_no, room_type, rate) values (501,'PENTHOUSE', 185.00), (502,'PENTHOUSE', 185.00);
6-insert into rooms( room_no, room_type, rate) values (503,'PREMIER PLUS', 143.00);
7- select count(room_no)
from reservations where checkin_date between '2020-08-01'and '2020-08-31'
Comment on lines +16 to +17
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@zoltan-gal zoltan-gal Oct 14, 2020

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More precisely count(distinct room_no), otherwise, you will get how many times rooms were occupied. distinct keyword removes duplicates before counting so that we will get how many different rooms were occupied.

8- select sum(checkout_date - checkin_date) from reservations where room_no between 201 and 299;
9- select count(*), sum(total), avg(total) from invoices where total >300;
10- select sum(checkout_date - checkin_date) from reservations group by room_no/100 ;
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@zoltan-gal zoltan-gal Oct 14, 2020

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Very elegant solution! One more advice, it could be made more information by adding a floor number to the query.
E.g.: select trunc(room_no/100) AS floor, um(checkout_date - checkin_date) from reservations group by room_no/100;

```

When you have finished all of the questions - open a pull request with your answers to the `Databases-Homework` repository.

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46 changes: 45 additions & 1 deletion week-2/mandatory/2-ecommerce-db/task.md
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Expand Up @@ -33,18 +33,62 @@ Open the file `cyf_ecommerce.sql` in VSCode and examine the SQL code. Take a pie
## Task

Once you understand the database that you are going to work with, solve the following challenge by writing SQL queries using everything you learned about SQL:

1. Retrieve all the customers' names and addresses who live in the United States
select name, address from customers where country ='United States';

2. Retrieve all the customers in ascending name sequence
select * from customers order by name ;

3. Retrieve all the products whose name contains the word `socks`
select * from products where product_name like '%socks%';

4. Retrieve all the products which cost more than 100 showing product id, name, unit price and supplier id.
select a.prod_id, p.product_name, a.unit_price, a.supp_id from products p join product_availability a on (a.prod_id = p.id) where a.unit_price >100 ;

5. Retrieve the 5 most expensive products
select * from product_availability order by unit_price DESC limit 5;
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@zoltan-gal zoltan-gal Oct 14, 2020

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It's fine but would be nice to see product info as well.


6. Retrieve all the products with their corresponding suppliers. The result should only contain the columns `product_name`, `unit_price` and `supplier_name`
select p.product_name, a.unit_price, s.supplier_name from products p join product_availability a on (a.prod_id = p.id) join suppliers s on (a.supp_id = s.id) ;

7. Retrieve all the products sold by suppliers based in the United Kingdom. The result should only contain the columns `product_name` and `supplier_name`.
select p.product_name, s.supplier_name from products p join product_availability a on(a.prod_id = p.id) join suppliers s on (a.supp_id = s.id) where s.country = 'United Kingdom';

8. Retrieve all orders, including order items, from customer ID `1`. Include order id, reference, date and total cost (calculated as quantity * unit price).

select o.order_reference, o.order_date from orders o join order_items i on (i.order_id = o.id) join product_availability a on (a.prod_id = i.product_id) where o.customer_id = 1;
////////////I don't understand what they exactly want from this question ////////////////
Comment on lines +59 to +60
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@zoltan-gal zoltan-gal Oct 14, 2020

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Let's break it down

  • Retrieve all orders, including order items for the customer 1
  • Into the result, include:
    • order id,
    • order reference,
    • order date
    • total cost of the order
      that is calculated as sum of (product quantity * product unit price).

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@zoltan-gal zoltan-gal Oct 14, 2020

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You're on the right track. Just need to add some extra column such as order id and the figure to calculate to end price by grouping the same order.


9. Retrieve all orders, including order items, from customer named `Hope Crosby`
select o.* from orders o join customers c on (o. customer_id = c.id) where c.name = 'Hope Crosby';
////// what do yo mean by including order items ////////////////////////////
Comment on lines 62 to +64
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@zoltan-gal zoltan-gal Oct 14, 2020

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I assume order items refers to the order_items table.


10. Retrieve all the products in the order `ORD006`. The result should only contain the columns `product_name`, `unit_price` and `quantity`.
select p.product_name , a.unit_price, i.quantity from orders o join order_items i on(i.order_id = o.id) join product_availability a on (i.supplier_id = a.supp_id) join products p on (p.id = a. prod_id)
where o.order_reference = 'ORD006';
Comment on lines +67 to +68
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@zoltan-gal zoltan-gal Oct 14, 2020

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It might be more intuitive joining the product availability through the product table and also add a join condition for connecting product on product availability table (product_availability a on (a.prod_id = p.id and a.supp_id = i.supplier_id)) to ensure you get the right combination, otherwise, join product_availability a on (i.supplier_id = a.supp_id) will join non-corresponding product rows that are still from the same suppliers.

e.g.

select p.product_name, a.unit_price, i.quantity
  from orders o join
       order_items i on (i.order_id = o.id) join
       products p on (i.product_id = p.id) join
       product_availability a on (a.prod_id = p.id and a.supp_id = i.supplier_id)
  where o.order_reference = 'ORD006';


11. Retrieve all the products with their supplier for all orders of all customers. The result should only contain the columns `name` (from customer), `order_reference`, `order_date`, `product_name`, `supplier_name` and `quantity`.
select c.name, o.order_reference, o.order_date, s.supplier_name , i.quantity
from customers c join
orders o on(c.id= o.customer_id) join
order_items i on (o.id = i. order_id) join
products p on (i.product_id = p.id) join
suppliers s on (s.id =i.supplier_id);

12. Retrieve the names of all customers who bought a product from a supplier based in China.
select c.name from customers c join orders o on(c.id= o.customer_id) join
order_items i on (o.id = i. order_id) join
suppliers s on (s.id =i.supplier_id)
where s.country = 'China';
Comment on lines +79 to +82
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@zoltan-gal zoltan-gal Oct 14, 2020

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It's okay but as an improvement, it is worth adding a distinct to remove duplicates if we are not interested in how many orders a customer has had.

select distinct c.name
  from customers c join
       orders o on (o.customer_id = c.id) join
       order_items i on (i.order_id = o.id) join
       suppliers s on (i.supplier_id = s.id)
  where s.country = 'China';



13. List all orders giving customer name, order reference, order date and order total amount (quantity * unit price) in descending order of total.
select c.name, o.order_reference, o.order_date, sum (quantity * unit_price) as total
from customers c join orders o on(c.id= o.customer_id) join
order_items i on (o.id = i. order_id) join
product_availability a on (i.supplier_id = a.supp_id)
group by c.name, o.order_reference, o.order_date
ORDER BY totaL DESC ;
Comment on lines +86 to +91
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@zoltan-gal zoltan-gal Oct 14, 2020

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Basically, you did it here what hadn't understood here:

  1. Retrieve all orders, including order items, from customer ID 1. Include order id, reference, date and total cost (calculated as quantity * unit price).

select o.order_reference, o.order_date from orders o join order_items i on (i.order_id = o.id) join product_availability a on (a.prod_id = i.product_id) where o.customer_id = 1;
////////////I don't understand what they exactly want from this question ////////////////

The only problem with the query is the same as the aforementioned.
You should and also add a join condition for connecting products on product availability table (product_availability a on (a.prod_id = p.id and a.supp_id = i.supplier_id)) to ensure you get the right combination from that table, otherwise, it will join more rows than necessary and the result will be incorrect.

select c.name, o.order_reference, o.order_date, sum(i.quantity * a.unit_price) as total
 from customers c join
      orders o on (o.customer_id = c.id) join
      order_items i on (i.order_id = o.id) join
      product_availability a on (i.supplier_id = a.supp_id and i.product_id = a.prod_id)
 group by c.name, o.order_reference, o.order_date
 order by total desc;




1 change: 1 addition & 0 deletions week-3/mandatory/cyf-ecommerce-api/.gitignore
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node_modules
148 changes: 148 additions & 0 deletions week-3/mandatory/cyf-ecommerce-api/cyf_ecommerce.sql
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drop table if exists order_items;
drop table if exists orders;
drop table if exists customers;
drop table if exists products;
drop table if exists suppliers;

CREATE TABLE customers (
id SERIAL PRIMARY KEY,
name VARCHAR(50) NOT NULL,
address VARCHAR(120),
city VARCHAR(30),
country VARCHAR(20)
);

CREATE TABLE suppliers (
id SERIAL PRIMARY KEY,
supplier_name VARCHAR(100) NOT NULL,
country VARCHAR(20) NOT NULL
);

CREATE TABLE products (
id SERIAL PRIMARY KEY,
product_name VARCHAR(100) NOT NULL,
unit_price INT NOT NULL,
supplier_id INT REFERENCES suppliers(id)
);

CREATE TABLE orders (
id SERIAL PRIMARY KEY,
order_date DATE NOT NULL,
order_reference VARCHAR(10) NOT NULL,
customer_id INT REFERENCES customers(id)
);

CREATE TABLE order_items (
id SERIAL PRIMARY KEY,
order_id INT REFERENCES orders(id),
product_id INT REFERENCES products(id),
quantity INT NOT NULL
);

/////////////////////homework solution ////////////////////////
1-SELECT name, address FROM customers WHERE country ='United States';

2-SELECT * FROM customers ORDER BY name ;

3-SELECT * FROM products WHERE unit_price > 100;

4-SELECT * FROM products WHERE product_name LIKE '%socks%';

5-SELECT * FROM products
ORDER BY unit_price DESC
limit 5;

6-SELECT products.product_name, products.unit_price, supplier_name FROM products
INNER JOIN suppliers ON products.supplier_id = suppliers.id ;

7-SELECT products.product_name, supplier_name FROM products
INNER JOIN suppliers ON products.supplier_id = suppliers.id WHERE suppliers.country = 'United Kingdom';
8- SELECT * FROM orders WHERE id = 1;

9-SELECT orders.* , customers.name FROM orders
INNER JOIN customers ON orders.customer_id = customers.id WHERE customers.name = 'Hope Crosby';

10-SELECT products.product_name, products.unit_price, order_items.quantity ,orders.order_reference FROM order_items
INNER JOIN orders ON order_items.order_id = orders.id
INNER JOIN products ON order_items.product_id = products.id
WHERE orders.order_reference = 'ORD006';

11-SELECT customers.name, orders.order_reference, orders.order_date, products.product_name, suppliers.supplier_name , order_items.quantity FROM
customers INNER JOIN orders ON orders.customer_id = customers.id
INNER JOIN order_items ON order_items.order_id = orders.id
INNER JOIN products ON order_items.product_id = products.id
INNER JOIN suppliers ON products.supplier_id = suppliers.id;

12- SELECT DISTINCT customers.name FROM
customers INNER JOIN orders ON orders.customer_id = customers.id
INNER JOIN order_items ON order_items.order_id = orders.id
INNER JOIN products ON order_items.product_id = products.id
INNER JOIN suppliers ON products.supplier_id = suppliers.id
WHERE suppliers.country = 'China';
////////////////////////////////////////////////////////////////////////////////////////////////////////////////
INSERT INTO customers (name, address, city, country) VALUES ('Guy Crawford','770-2839 Ligula Road','Paris','France');
INSERT INTO customers (name, address, city, country) VALUES ('Hope Crosby','P.O. Box 276, 4976 Sit Rd.','Steyr','United Kingdom');
INSERT INTO customers (name, address, city, country) VALUES ('Britanney Kirkland','P.O. Box 577, 5601 Sem, St.','Little Rock','United Kingdom');
INSERT INTO customers (name, address, city, country) VALUES ('Amber Tran','6967 Ac Road','Villafranca Asti','United States');
INSERT INTO customers (name, address, city, country) VALUES ('Edan Higgins','Ap #840-3255 Tincidunt St.','Arles','United States');
INSERT INTO customers (name, address, city, country) VALUES ('Quintessa Austin','597-2737 Nunc Rd.','Saint-Marc','United Kingdom');

INSERT INTO suppliers (supplier_name, country) VALUES ('Amazon', 'United States');
INSERT INTO suppliers (supplier_name, country) VALUES ('Taobao', 'China');
INSERT INTO suppliers (supplier_name, country) VALUES ('Argos', 'United Kingdom');
INSERT INTO suppliers (supplier_name, country) VALUES ('Sainsburys', 'United Kingdom');

INSERT INTO products (product_name, unit_price, supplier_id) VALUES ('Tee Shirt Olympic Games', 20, 1);
INSERT INTO products (product_name, unit_price, supplier_id) VALUES ('Tee Shirt Olympic Games', 18, 2);
INSERT INTO products (product_name, unit_price, supplier_id) VALUES ('Tee Shirt Olympic Games', 21, 3);
INSERT INTO products (product_name, unit_price, supplier_id) VALUES ('Mobile Phone X', 299, 1);
INSERT INTO products (product_name, unit_price, supplier_id) VALUES ('Mobile Phone X', 249, 4);
INSERT INTO products (product_name, unit_price, supplier_id) VALUES ('Super warm socks', 10, 1);
INSERT INTO products (product_name, unit_price, supplier_id) VALUES ('Super warm socks', 5, 2);
INSERT INTO products (product_name, unit_price, supplier_id) VALUES ('Super warm socks', 8, 3);
INSERT INTO products (product_name, unit_price, supplier_id) VALUES ('Super warm socks', 10, 4);
INSERT INTO products (product_name, unit_price, supplier_id) VALUES ('Le Petit Prince', 10, 1);
INSERT INTO products (product_name, unit_price, supplier_id) VALUES ('Le Petit Prince', 10, 4);
INSERT INTO products (product_name, unit_price, supplier_id) VALUES ('Ball', 14, 1);
INSERT INTO products (product_name, unit_price, supplier_id) VALUES ('Ball', 15, 4);
INSERT INTO products (product_name, unit_price, supplier_id) VALUES ('Ball', 20, 2);
INSERT INTO products (product_name, unit_price, supplier_id) VALUES ('Javascript Book', 40, 1);
INSERT INTO products (product_name, unit_price, supplier_id) VALUES ('Javascript Book', 39, 3);
INSERT INTO products (product_name, unit_price, supplier_id) VALUES ('Javascript Book', 41, 2);
INSERT INTO products (product_name, unit_price, supplier_id) VALUES ('Coffee Cup', 3, 1);
INSERT INTO products (product_name, unit_price, supplier_id) VALUES ('Coffee Cup', 4, 2);
INSERT INTO products (product_name, unit_price, supplier_id) VALUES ('Coffee Cup', 4, 3);
INSERT INTO products (product_name, unit_price, supplier_id) VALUES ('Coffee Cup', 5, 4);

INSERT INTO orders (order_date, order_reference, customer_id) VALUES ('2019-06-01', 'ORD001', 1);
INSERT INTO orders (order_date, order_reference, customer_id) VALUES ('2019-07-15', 'ORD002', 1);
INSERT INTO orders (order_date, order_reference, customer_id) VALUES ('2019-07-11', 'ORD003', 1);
INSERT INTO orders (order_date, order_reference, customer_id) VALUES ('2019-05-24', 'ORD004', 2);
INSERT INTO orders (order_date, order_reference, customer_id) VALUES ('2019-05-30', 'ORD005', 3);
INSERT INTO orders (order_date, order_reference, customer_id) VALUES ('2019-07-05', 'ORD006', 4);
INSERT INTO orders (order_date, order_reference, customer_id) VALUES ('2019-04-05', 'ORD007', 4);
INSERT INTO orders (order_date, order_reference, customer_id) VALUES ('2019-07-23', 'ORD008', 5);
INSERT INTO orders (order_date, order_reference, customer_id) VALUES ('2019-07-24', 'ORD009', 5);
INSERT INTO orders (order_date, order_reference, customer_id) VALUES ('2019-05-10', 'ORD010', 5);

INSERT INTO order_items (order_id, product_id, quantity) VALUES(1, 2, 1);
INSERT INTO order_items (order_id, product_id, quantity) VALUES(1, 7, 5);
INSERT INTO order_items (order_id, product_id, quantity) VALUES(2, 8, 4);
INSERT INTO order_items (order_id, product_id, quantity) VALUES(2, 11, 1);
INSERT INTO order_items (order_id, product_id, quantity) VALUES(3, 20, 10);
INSERT INTO order_items (order_id, product_id, quantity) VALUES(3, 14, 2);
INSERT INTO order_items (order_id, product_id, quantity) VALUES(4, 4, 1);
INSERT INTO order_items (order_id, product_id, quantity) VALUES(5, 16, 2);
INSERT INTO order_items (order_id, product_id, quantity) VALUES(5, 10, 1);
INSERT INTO order_items (order_id, product_id, quantity) VALUES(6, 19, 3);
INSERT INTO order_items (order_id, product_id, quantity) VALUES(6, 17, 1);
INSERT INTO order_items (order_id, product_id, quantity) VALUES(6, 11, 1);
INSERT INTO order_items (order_id, product_id, quantity) VALUES(6, 9, 3);
INSERT INTO order_items (order_id, product_id, quantity) VALUES(7, 8, 15);
INSERT INTO order_items (order_id, product_id, quantity) VALUES(8, 1, 1);
INSERT INTO order_items (order_id, product_id, quantity) VALUES(8, 5, 1);
INSERT INTO order_items (order_id, product_id, quantity) VALUES(9, 13, 2);
INSERT INTO order_items (order_id, product_id, quantity) VALUES(10, 14, 1);
INSERT INTO order_items (order_id, product_id, quantity) VALUES(10, 6, 5);


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