databases_basic.md

      

Relational Databases Basics

Theory

• Introduction To DBMS
• SQL Introduction
• Intro to Relational Databases
• CodeCademy Learn SQL
• Intro to SQL: Querying and managing data

Practical Task

1. Seed data is data that you populate the database with at the time it is created. Assume that the following script was used to create tables and produce seed data:

CREATE TABLE IF NOT EXISTS `person` (
    `id` INT AUTO_INCREMENT PRIMARY KEY,
    `first_name` VARCHAR(255) NOT NULL,
    `last_name` VARCHAR(255) NOT NULL,
    `created_at` DATETIME DEFAULT NOW(),
    `updated_at` DATETIME DEFAULT NOW()
)  ENGINE=INNODB;

CREATE TABLE IF NOT EXISTS `item` (
    `id` INT AUTO_INCREMENT PRIMARY KEY,
    `name` VARCHAR(255) NOT NULL,
    `price` DECIMAL(5,2) DEFAULT 0,
    `created_at` DATETIME DEFAULT NOW(),
    `updated_at` DATETIME DEFAULT NOW()
)  ENGINE=INNODB;

CREATE TABLE IF NOT EXISTS `order` (
    `id` INT AUTO_INCREMENT PRIMARY KEY,
    `person_id` INT NOT NULL REFERENCES `person`(`id`),
    `created_at` DATETIME DEFAULT NOW(),
    `updated_at` DATETIME DEFAULT NOW()
)  ENGINE=INNODB;

CREATE TABLE IF NOT EXISTS `order_item` (
    `id` INT AUTO_INCREMENT PRIMARY KEY,
    `order_id` INT NOT NULL REFERENCES `order`(`id`),
    `item_id` INT NOT NULL REFERENCES `item_id`(`id`),
    `quantity` INT DEFAULT 1,
    `discount` DECIMAL(5,2) DEFAULT 0,
    `created_at` DATETIME DEFAULT NOW(),
    `updated_at` DATETIME DEFAULT NOW()
)  ENGINE=INNODB;

INSERT INTO `person`(`first_name`, `last_name`) VALUES
    ('Ann', 'Peterson'),
    ('Josh', 'Harris'),
    ('Sarah', 'Connor'),
    ('James', 'Ball');

INSERT INTO `item`(`name`, `price`) VALUES
    ('TV', 299.99),
    ('Carrot', 1.25),
    ('Patrol', 1.41),
    ('Soap', 0.4),
    ('Football Tickets', 149),
    ('T-Shirt', 19.1),
    ('Playstation 4 Pro', 419.99);

INSERT INTO `order`(`person_id`) VALUES
    (1),
    (2),
    (4),
    (4);

INSERT INTO `order_item`(`order_id`, `item_id`, `quantity`, `discount`) VALUES
    (1, 3, 4, 0),
    (1, 6, 1, 0),
    (2, 1, 1, 11.2),
    (2, 7, 1, 15.99),
    (3, 4, 3, 0),
    (3, 2, 8, 0),
    (3, 6, 1, 0),
    (4, 5, 1, 1.49);

2. Create folder called sql_basics in your kottans-backend repo

3. In sql_basics folder create file called select.sql and write SQL SELECT statement to get following output:

first_name	last_name	total_orders	total_items_bought	total_money_spent
Ann	Peterson	1	5	24.74
Josh	Harris	1	2	692.79
Sarah	Connor	0	null	null
James	Ball	2	13	177.81

4. Note that discount column value reduces order_item price for each item.
5. Use DB Fiddle for practice.

Additional Materials

• How does a relational database work

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