added create_tables and inser_data files

skonev/postgresql/create_tables.sql

@@ -0,0 +1,45 @@
+BEGIN;
+
+CREATE TABLE SKONEV.users(
+	id INT PRIMARY KEY, 
+	name VARCHAR(100), 
+	age INT, 
+	email VARCHAR(255) UNIQUE, 
+	registration_date DATE NOT NULL
+	);
+
+CREATE TABLE SKONEV.courses(
+	id INT PRIMARY KEY,
+	title TEXT NOT NULL,
+	category VARCHAR(255) CHECK (category IN ('data', 'programming', 'business')),
+	created_at DATE NOT NULL
+	);
+
+CREATE TABLE SKONEV.lessons(
+	id INT PRIMARY KEY, 
+	course_id INT NOT NULL,
+	FOREIGN KEY (course_id) REFERENCES courses(id), 
+	title TEXT NOT NULL, 
+	duration_min INT NOT NULL
+	);
+
+
+CREATE TABLE SKONEV.enrollments(
+	id INT PRIMARY KEY, 
+	user_id INT NOT NULL,
+	FOREIGN KEY (user_id) REFERENCES users(id), 
+	course_id INT NOT NULL,
+	FOREIGN KEY (course_id) REFERENCES courses(id), 
+	enrolled_at DATE NOT NULL
+	);
+
+CREATE TABLE SKONEV.lesson_views(
+	id INT PRIMARY KEY, 
+	user_id INT NOT NULL,
+	FOREIGN KEY (user_id) REFERENCES users(id), 
+	lesson_id INT NOT NULL,
+	FOREIGN KEY (lesson_id) REFERENCES lessons(id), 
+	viewed_at TIMESTAMP NOT NULL
+	);
+
+COMMIT;