Lesson 8

Lesson-7/Task1.sql

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+DROP DATABASE `social_network`;
+CREATE DATABASE `social_network`;
+USE `social_network`;
+CREATE TABLE `social_network`.`users` (
+    `id_user` MEDIUMINT NOT NULL AUTO_INCREMENT,
+    `first_name` VARCHAR(100) NOT NULL,
+    `last_name` VARCHAR(100) NOT NULL,
+    PRIMARY KEY (`id_user`)
+);
+
+INSERT INTO `social_network`.`users` (`id_user`, `first_name`, `last_name`) VALUES ('1', 'Max', 'Maximov'), ('2', 'Andrey', 'Andreev'), ('3', 'Ivan', 'Ivanov'), ('4', 'Peter', 'Peterson');
+
+CREATE TABLE `social_network`.`likes` (
+   `from_user` MEDIUMINT NOT NULL,
+   `to_user` MEDIUMINT NOT NULL,
+   PRIMARY KEY (`from_user`, `to_user`),
+   INDEX `fk_to_user_idx` (`to_user` ASC) VISIBLE,
+   CONSTRAINT `fk_from_user`
+     FOREIGN KEY (`from_user`)
+     REFERENCES `social_network`.`users` (`id_user`)
+     ON DELETE NO ACTION
+     ON UPDATE NO ACTION,
+   CONSTRAINT `fk_to_user`
+     FOREIGN KEY (`to_user`)
+     REFERENCES `social_network`.`users` (`id_user`)
+     ON DELETE NO ACTION
+     ON UPDATE NO ACTION);
+
+INSERT INTO `social_network`.`likes` (`from_user`, `to_user`) VALUES (1, 2), (1, 3), (1, 4), (2, 1), (2, 3), (3, 1), (3, 4), (4, 1), (4, 2), (4, 3);
+
+-- Задача 1. У вас есть социальная сеть, где пользователи (id, имя) могут ставить друг другу лайки. 
+-- Создайте необходимые таблицы для хранения данной информации. 
+-- Создайте запрос, который выведет информацию:
+-- id пользователя;
+-- имя;
+-- лайков получено;
+-- лайков поставлено;
+-- взаимные лайки.
+
+SELECT 
+    users.id_user,
+    users.first_name AS `first name`,
+    users.last_name AS `last name`,
+    COUNT(DISTINCT l2.from_user) AS `like get`,
+    COUNT(DISTINCT l1.to_user) AS `like sent`,
+    SUM(IF(l1.to_user = l2.from_user, 1, 0)) AS `croos like`
+FROM
+    users
+        JOIN
+    likes AS l1 ON users.id_user = l1.from_user
+        JOIN
+    likes AS l2 ON users.id_user = l2.to_user
+GROUP BY users.id_user;
+ ;
+
+-- Задача 2. Для структуры из задачи 1 выведите список всех пользователей, 
+-- которые поставили лайк пользователям A и B (id задайте произвольно), 
+-- но при этом не поставили лайк пользователю C.
+
+SELECT 
+    from_user,
+    SUM(IF(to_user = 1, 1, 0)) AS t1,
+    SUM(IF(to_user = 2, 1, 0)) AS t2,
+    SUM(IF(to_user = 3, 1, 0)) AS t3
+FROM
+    likes
+GROUP BY from_user
+HAVING (t1 = 1 AND t2 = 1 AND t3 = 0)
+;
+
+-- Задача 3. Добавим сущности «Фотография» и «Комментарии к фотографии». 
+-- Нужно создать функционал для пользователей, который позволяет ставить лайки не только пользователям, 
+-- но и фото или комментариям к фото. Учитывайте следующие ограничения:
+-- пользователь не может дважды лайкнуть одну и ту же сущность;
+-- пользователь имеет право отозвать лайк;
+-- необходимо иметь возможность считать число полученных сущностью лайков и выводить список пользователей, поставивших лайки;
+-- в будущем могут появиться новые виды сущностей, которые можно лайкать.
+
+ CREATE TABLE `social_network`.`photo` (
+   `id_photo` MEDIUMINT NOT NULL AUTO_INCREMENT,
+   `url` VARCHAR(500) NULL,
+   `id_user` MEDIUMINT NOT NULL,
+   PRIMARY KEY (`id_photo`),
+   INDEX `fk_id_user_photo_idx` (`id_user` ASC) VISIBLE,
+   CONSTRAINT `fk_id_user_photo`
+     FOREIGN KEY (`id_user`)
+     REFERENCES `social_network`.`users` (`id_user`)
+     ON DELETE NO ACTION
+     ON UPDATE NO ACTION);
+
+ CREATE TABLE `social_network`.`comment_photo` (
+   `id_comment` MEDIUMINT NOT NULL AUTO_INCREMENT,
+   `comment` VARCHAR(500) NULL,
+   `id_user` MEDIUMINT NOT NULL,
+   `id_photo` MEDIUMINT NOT NULL,
+   UNIQUE INDEX `id_photo_UNIQUE` (`id_photo` ASC) VISIBLE,
+   PRIMARY KEY (`id_comment`),
+   INDEX `fk_id_user_comment_idx` (`id_user` ASC) VISIBLE,
+   CONSTRAINT `fk_id_user_comment`
+     FOREIGN KEY (`id_user`)
+     REFERENCES `social_network`.`users` (`id_user`)
+     ON DELETE NO ACTION
+     ON UPDATE NO ACTION,
+   CONSTRAINT `fk_id_photo_comment`
+     FOREIGN KEY (`id_photo`)
+     REFERENCES `social_network`.`photo` (`id_photo`)
+     ON DELETE NO ACTION
+     ON UPDATE NO ACTION);
+;
+ insert into `social_network`.`photo` (`id_user`) values (1), (2), (3);
+;
+ drop table likes;
+;
+CREATE TABLE `likes` (
+    id_user MEDIUMINT,
+    like_to_user MEDIUMINT,
+    like_to_photo MEDIUMINT,
+    like_to_comment MEDIUMINT,
+    UNIQUE KEY `user_id_photo` (`id_user` , `like_to_photo`),
+    UNIQUE KEY `user_id_comment` (`id_user` , `like_to_comment`),
+    UNIQUE KEY `user_id_user` (`id_user` , `like_to_user`),
+    CONSTRAINT `fk_id_like_to_user` FOREIGN KEY (`like_to_user`)
+        REFERENCES `social_network`.`users` (`id_user`)
+        ON DELETE NO ACTION ON UPDATE NO ACTION,
+    CONSTRAINT `fk_id_like_to_photo` FOREIGN KEY (`like_to_photo`)
+        REFERENCES `social_network`.`photo` (`id_photo`)
+        ON DELETE NO ACTION ON UPDATE NO ACTION,
+    CONSTRAINT `fk_id_like_to_comment` FOREIGN KEY (`like_to_comment`)
+        REFERENCES `social_network`.`comment_photo` (`id_comment`)
+        ON DELETE NO ACTION ON UPDATE NO ACTION
+);
+
+INSERT INTO `social_network`.`likes` (`id_user`, `like_to_user`) VALUES (1, 2), (1, 3), (1, 4), (2, 1), (2, 3), (3, 1), (3, 4), (4, 1), (4, 2), (4, 3);
+
+INSERT INTO `social_network`.`likes` (`id_user`, `like_to_photo`) VALUES (1, 2), (2, 2), (2, 3), (3, 3);
+
+SELECT 
+    users.id_user,
+    users.first_name AS `first name`,
+    users.last_name AS `last name`,
+    COUNT(DISTINCT l1.id_user) likes_get,
+    COUNT(DISTINCT l2.like_to_user) likes_sent,
+    SUM(IF(l1.id_user = l2.like_to_user, 1, 0)) cross_like
+FROM
+    users
+        LEFT JOIN
+    likes l1 ON users.id_user = l1.like_to_user
+        LEFT JOIN
+    likes l2 ON users.id_user = l2.id_user
+GROUP BY users.id_user;
+
+SELECT 
+    id_user,
+    SUM(IF(like_to_user = 1, 1, 0)) t1,
+    SUM(IF(like_to_user = 2, 1, 0)) t2,
+    SUM(IF(like_to_user = 3, 1, 0)) t3
+FROM
+    likes
+GROUP BY id_user
+HAVING (t1 = 1 AND t2 = 1 AND t3 = 0);