CREATE TABLE users (
id BIGINT NOT NULL PRIMARY KEY AUTO_INCREMENT,
username NVARCHAR(30) NOT NULL UNIQUE,
password NVARCHAR(50) NOT NULL
)

CREATE TABLE sections (
id BIGINT NOT NULL PRIMARY KEY AUTO_INCREMENT,
name NVARCHAR(50) NOT NULL UNIQUE,
)

CREATE TABLE posts (
id BIGINT NOT NULL PRIMARY KEY AUTO_INCREMENT,
description NVARCHAR(255) NOT NULL,
image_url NVARCHAR(255) NOT NULL,
date_time DATETIME DEFAULT CURRENT_TIMESTAMP,
author_id BIGINT NOT NULL,
section_id BIGINT NOT NULL,
CONSTRAINT FK_userId_users_posts FOREIGN KEY(author_id) REFERENCES users(id),
CONSTRAINT FK_sectionId_sections FOREIGN KEY(section_id) REFERENCES sections(id)
)

CREATE TABLE tags (
id BIGINT NOT NULL PRIMARY KEY AUTO_INCREMENT,
name VARCHAR(50) NOT NULL
)

CREATE TABLE comments (
id BIGINT NOT NULL PRIMARY KEY AUTO_INCREMENT,
description NVARCHAR(1000) NOT NULL,
date_time DATETIME DEFAULT CURRENT_TIMESTAMP,
author_id BIGINT NOT NULL,
post_id BIGINT NOT NULL,
CONSTRAINT FK_userId_users_comments FOREIGN KEY(author_id) REFERENCES users(id),
CONSTRAINT FK_postId_posts_comments FOREIGN KEY(post_id) REFERENCES posts(id)
)

CREATE TABLE post_tag (
post_id BIGINT NOT NULL,
tag_id BIGINT NOT NULL,
CONSTRAINT PK_postId_examId PRIMARY KEY(post_id, tag_id),
CONSTRAINT FK_postId_posts FOREIGN KEY(post_id) REFERENCES posts(id),
CONSTRAINT FK_tagId_tags FOREIGN KEY (tag_id) REFERENCES tags(id)
)

CREATE TABLE rating_posts_users (
post_id BIGINT NOT NULL,
user_id BIGINT NOT NULL,
grade INT NOT NULL,
CONSTRAINT PK_raiting_posts_users PRIMARY KEY(post_id, user_id),
CONSTRAINT FK_postId_userId_posts FOREIGN KEY (post_id) REFERENCES posts(id),
CONSTRAINT FK_postId_userId_users FOREIGN KEY (user_id) REFERENCES users(id),
CONSTRAINT CHK_gradeValue CHECK (grade = -1 OR grade = 1)
)