add one to many relationship

Author: ptyadana

Ultimate MySQL/12.One To Many.sql

@@ -0,0 +1,169 @@
+/* data prep*/
+CREATE TABLE customers(
+	id INT AUTO_INCREMENT PRIMARY KEY,
+	first_name VARCHAR(100) NOT NULL,
+	last_name VARCHAR(100) NOT NULL,
+	email VARCHAR(100) NOT NULL
+);
+
+CREATE TABLE orders(
+    id INT AUTO_INCREMENT PRIMARY KEY,
+    order_date DATE,
+    amount DECIMAL(8,2),
+    customer_id INT,
+    FOREIGN KEY(customer_id) REFERENCES customers(id)
+);
+
+INSERT INTO customers (first_name, last_name, email) 
+VALUES ('Boy', 'George', '[email protected]'),
+       ('George', 'Michael', '[email protected]'),
+       ('David', 'Bowie', '[email protected]'),
+       ('Blue', 'Steele', '[email protected]'),
+       ('Bette', 'Davis', '[email protected]');
+       
+INSERT INTO orders (order_date, amount, customer_id)
+VALUES ('2016/02/10', 99.99, 1),
+       ('2017/11/11', 35.50, 1),
+       ('2014/12/12', 800.67, 2),
+       ('2015/01/03', 12.50, 2),
+       ('1999/04/11', 450.25, 5);
+
+/*customers by spending high to low order */
+/*send them loyality programs,etc*/
+SELECT first_name, last_name,SUM(amount) AS total_spending
+FROM customers
+JOIN orders ON customers.id = orders.customer_id
+GROUP BY customers.id
+ORDER BY total_spending DESC;
+
+
+/* customers who haven't spent anything or ordered anything yet */
+/*we can send out discount cupons.. etc*/
+SELECT first_name, last_name,amount
+FROM customers
+LEFT JOIN orders ON customers.id = orders.customer_id
+WHERE orders.customer_id IS NULL;
+
+/*-------------------------------------------*/
+
+/*------------------ Challenges -------------------------*/
+CREATE TABLE students(
+	id INT AUTO_INCREMENT PRIMARY KEY,
+	first_name VARCHAR(150)
+);
+
+
+CREATE TABLE papers(
+	title VARCHAR(150) NOT NULL,
+	grade INT NOT NULL,
+	student_id INT,
+	FOREIGN KEY(student_id) REFERENCES students(id) ON DELETE CASCADE
+);
+
+INSERT INTO students (first_name) VALUES 
+('Caleb'), ('Samantha'), ('Raj'), ('Carlos'), ('Lisa');
+
+INSERT INTO papers (student_id, title, grade ) VALUES
+(1, 'My First Book Report', 60),
+(1, 'My Second Book Report', 75),
+(2, 'Russian Lit Through The Ages', 94),
+(2, 'De Montaigne and The Art of The Essay', 98),
+(4, 'Borges and Magical Realism', 89);
+
+
+/*----------------------*/
+/*
++------------+---------------------------------------+-------+
+| first_name | title                                 | grade |
++------------+---------------------------------------+-------+
+| Samantha   | De Montaigne and The Art of The Essay |    98 |
+| Samantha   | Russian Lit Through The Ages          |    94 |
+| Carlos     | Borges and Magical Realism            |    89 |
+| Caleb      | My Second Book Report                 |    75 |
+| Caleb      | My First Book Report                  |    60 |
++------------+---------------------------------------+-------+
+*/
+SELECT first_name, title,grade
+FROM students
+JOIN papers ON students.id = papers.student_id
+ORDER BY grade DESC;
+
+/*
++------------+---------------------------------------+-------+
+| first_name | title                                 | grade |
++------------+---------------------------------------+-------+
+| Caleb      | My First Book Report                  |    60 |
+| Caleb      | My Second Book Report                 |    75 |
+| Samantha   | Russian Lit Through The Ages          |    94 |
+| Samantha   | De Montaigne and The Art of The Essay |    98 |
+| Raj        | NULL                                  |  NULL |
+| Carlos     | Borges and Magical Realism            |    89 |
+| Lisa       | NULL                                  |  NULL |
++------------+---------------------------------------+-------+
+*/
+SELECT first_name, title, grade
+FROM students
+LEFT JOIN papers ON students.id = papers.student_id;
+
+
+/*
++------------+---------------------------------------+-------+
+| first_name | title                                 | grade |
++------------+---------------------------------------+-------+
+| Caleb      | My First Book Report                  | 60    |
+| Caleb      | My Second Book Report                 | 75    |
+| Samantha   | Russian Lit Through The Ages          | 94    |
+| Samantha   | De Montaigne and The Art of The Essay | 98    |
+| Raj        | MISSING                               | 0     |
+| Carlos     | Borges and Magical Realism            | 89    |
+| Lisa       | MISSING                               | 0     |
++------------+---------------------------------------+-------+
+*/
+SELECT first_name, 
+	IFNULL(title,'MISSING'), 
+	IFNULL(grade,0)
+FROM students
+LEFT JOIN papers ON students.id = papers.student_id;
+
+
+/*
++------------+---------+
+| first_name | average |
++------------+---------+
+| Samantha   | 96.0000 |
+| Carlos     | 89.0000 |
+| Caleb      | 67.5000 |
+| Raj        | 0       |
+| Lisa       | 0       |
++------------+---------+
+*/
+SELECT first_name,
+	IFNULL(AVG(grade),0) AS average
+FROM students
+LEFT JOIN papers ON students.id = papers.student_id
+GROUP BY students.id
+ORDER BY average DESC;
+
+
+/*
++------------+---------+----------------+
+| first_name | average | passing_status |
++------------+---------+----------------+
+| Samantha   | 96.0000 | PASSING        |
+| Carlos     | 89.0000 | PASSING        |
+| Caleb      | 67.5000 | FAILING        |
+| Raj        | 0       | FAILING        |
+| Lisa       | 0       | FAILING        |
++------------+---------+----------------+
+*/
+SELECT first_name,
+	IFNULL(AVG(grade),0) AS average,
+	CASE
+		WHEN AVG(grade) >= 75 THEN 'PASSING'
+		WHEN AVG(grade) IS NULL THEN 'FAILING'
+		ELSE 'FAILING'
+	END AS passing_status
+FROM students
+LEFT JOIN papers ON students.id = papers.student_id
+GROUP BY students.id
+ORDER BY average DESC;