--drop table is exists users;
create table users(
	id int primary key,
	name varchar(50) not null,
	age int not null,
	email varchar(50) not null,
	registration_date date not null default current_date
)

insert into users (id, name, age, email, registration_date) values
(1,	'Alice',	25,	'alice@mail.com',	    '2023-01-10'),
(2,	'Bob',	30,	'bob@gmail.com',	    '2023-02-05'),
(3,	'Charlie',22,	'charlie@mail.com',    '2023-02-20'),
(4,	'Diana',	28,	'diana@mail.com',	    '2023-03-01'),
(5,	'Ethan',	35,	'ethan@gmail.com', '2023-03-10')

create table courses(
    id int primary key,
    title text not null,
    category varchar(30) not null,
    created_at date not null default current_date
)

insert into courses (id, title, category, created_at) values
(1,	'SQL для начинающих',	'data',	'2023-01-01'),
(2,	'Python для анализа данных',	'programming',	'2023-01-15'),
(3,	'BI с нуля', 'business',	'2023-03-01');

create table lessons(
    id int primary key,
    course_id int references courses(id), 
    title text not null,
    duration_min int
)

insert into lessons (id, course_id, title, duration_min) values
(1,	1,	'SELECT и FROM',	10),
(2,	1,	'JOIN',	15),
(3,	2,	'Pandas',	20),
(4,	3,	'Основы BI',	12),
(5,	3,	'Метрики и дашборды',	18)

create table enrollments(
    id int primary key,
    user_id int references users(id),
    course_id int references courses(id),
    enrolled_at date not null default current_date
)

insert into enrollments (id, user_id, course_id, enrolled_at) values
(1,	1,	1,	'2023-01-15'),
(2,	1,	2,	'2023-02-01'),
(3,	2,	1,	'2023-01-20'),
(4,	3,	2,	'2023-03-05'),
(5,	4,	3,	'2023-04-01')

create table lessons_views(
    id int primary key,
    user_id int references users(id),
    lesson_id int references lessons(id),
    viewed_at timestamp not null default now()
)

insert into lessons_views(id, user_id, lesson_id, viewed_at) values
(1,	1,	1,	'2023-01-16 10:00:00'),
(2,	1,	2,	'2023-01-16 10:15:00'),
(3,	2,	1,	'2023-01-21 09:00:00'),
(4,	3,	3,	'2023-03-06 12:00:00'),
(5,	4,	4,	'2023-04-02 10:00:00'),
(6,	4,	5,	'2023-04-03 10:00:00')