ig_clone db challenges

Author: mayankSystems

src/main/java/dev/mayankg/db_concepts/mysql/ig_clone_db/ig_clone_challenges.sql

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+-- 1. Find the 5 oldest users.
+SELECT *
+FROM users
+ORDER BY created_at ASC
+LIMIT 5;
+
+-- 2. What day of the week do most users register on?
+SELECT
+    DAYNAME(created_at) AS day_of_week,
+    COUNT(*) AS new_users
+FROM users
+GROUP BY day_of_week
+ORDER BY new_users DESC
+LIMIT 1;
+
+-- 3. Find the users who have never posted a photo.
+-- Option 1
+SELECT *
+FROM users
+WHERE id NOT IN (
+    SELECT user_id
+    FROM photos
+    GROUP BY user_id
+);
+
+-- Option 2
+SELECT
+    username
+FROM users u
+LEFT JOIN photos p ON u.id = p.user_id
+WHERE p.user_id IS NULL;
+
+-- 4. Which user has the most likes on a single photo?
+SELECT
+    p.id,
+    u.username,
+    p.image_url,
+    lp.like_count
+FROM photos p
+RIGHT JOIN (
+    SELECT
+        photo_id,
+        COUNT(*) AS like_count
+    FROM likes
+    GROUP BY photo_id
+    ORDER BY like_count DESC
+) AS lp ON p.id = lp.photo_id
+INNER JOIN users u ON u.id = p.user_id
+LIMIT 1;
+
+-- 5.1. How many times does the average user post (excludes users who have never posted)?
+SELECT
+    COUNT(*) / COUNT(DISTINCT user_id) AS avg_post_per_user
+FROM photos;
+
+-- 5.2. How many times does the average user post (includes users who have never posted)?
+SELECT
+    (SELECT COUNT(*) FROM photos) / (SELECT COUNT(*) FROM users) AS avg_post_per_user;
+
+-- 6. What are the top 5 most commonly used hashtags?
+SELECT
+    pt.tag_id,
+    t.tag_name,
+    COUNT(*) AS used
+FROM photo_tags pt
+LEFT JOIN tags t ON pt.tag_id = t.id
+GROUP BY pt.tag_id, t.tag_name
+ORDER BY used DESC
+LIMIT 5;
+
+-- 7. Find the users who have liked every single photo on the site.
+SELECT
+    l.user_id,
+    u.username,
+    COUNT(*) AS total
+FROM users u
+RIGHT JOIN likes l ON u.id = l.user_id
+GROUP BY l.user_id, u.username
+HAVING total = (SELECT COUNT(*) FROM photos);