Lab 8 extra of unit 9 done

Lab 8 Extra.sql

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+USE sakila
+
+-- Challenge 1
+-- Ranking films by their length
+SELECT
+    title,
+    length,
+    RANK() OVER (ORDER BY length DESC) AS film_rank
+FROM film
+WHERE length IS NOT NULL
+  AND length > 0;
+
+-- Ranking films by length within each rating category
+SELECT
+    title,
+    length,
+    rating,
+    RANK() OVER (
+        PARTITION BY rating
+        ORDER BY length DESC
+    ) AS film_rank
+FROM film
+WHERE length IS NOT NULL
+  AND length > 0;
+
+-- For each film, show the actor/actress with the greatest number of film appearances
+WITH actor_film_count AS (
+    SELECT
+        actor_id,
+        COUNT(*) AS total_films
+    FROM film_actor
+    GROUP BY actor_id
+),
+film_actor_rank AS (
+    SELECT
+        f.film_id,
+        f.title,
+        a.actor_id,
+        CONCAT(a.first_name, ' ', a.last_name) AS actor_name,
+        afc.total_films,
+        RANK() OVER (
+            PARTITION BY f.film_id
+            ORDER BY afc.total_films DESC
+        ) AS actor_rank
+    FROM film AS f
+    JOIN film_actor AS fa
+        ON f.film_id = fa.film_id
+    JOIN actor AS a
+        ON fa.actor_id = a.actor_id
+    JOIN actor_film_count AS afc
+        ON a.actor_id = afc.actor_id
+)
+SELECT
+    title,
+    actor_name,
+    total_films
+FROM film_actor_rank
+WHERE actor_rank = 1
+ORDER BY title;
+
+-- Challenge 2
+-- Monthly active customers
+WITH monthly_active AS (
+    SELECT
+        DATE_FORMAT(rental_date, '%Y-%m') AS month,
+        COUNT(DISTINCT customer_id) AS active_customers
+    FROM rental
+    GROUP BY DATE_FORMAT(rental_date, '%Y-%m')
+)
+SELECT *
+FROM monthly_active
+ORDER BY month;
+
+-- Active customers in the previous month
+WITH monthly_active AS (
+    SELECT
+        DATE_FORMAT(rental_date, '%Y-%m') AS month,
+        COUNT(DISTINCT customer_id) AS active_customers
+    FROM rental
+    GROUP BY DATE_FORMAT(rental_date, '%Y-%m')
+)
+SELECT
+    month,
+    active_customers,
+    LAG(active_customers) OVER (ORDER BY month) AS previous_month_active
+FROM monthly_active
+ORDER BY month;
+
+-- Percentage change in active customers
+WITH monthly_active AS (
+    SELECT
+        DATE_FORMAT(rental_date, '%Y-%m') AS month,
+        COUNT(DISTINCT customer_id) AS active_customers
+    FROM rental
+    GROUP BY DATE_FORMAT(rental_date, '%Y-%m')
+)
+SELECT
+    month,
+    active_customers,
+    LAG(active_customers) OVER (ORDER BY month) AS previous_month_active,
+    ROUND(
+        (
+            active_customers -
+            LAG(active_customers) OVER (ORDER BY month)
+        ) * 100.0 /
+        LAG(active_customers) OVER (ORDER BY month),
+        2
+    ) AS percentage_change
+FROM monthly_active
+ORDER BY month;
+
+-- Retained customers
+WITH customer_month AS (
+    SELECT DISTINCT
+        customer_id,
+        DATE_FORMAT(rental_date, '%Y-%m') AS month
+    FROM rental
+)
+SELECT
+    c1.month,
+    COUNT(DISTINCT c1.customer_id) AS retained_customers
+FROM customer_month c1
+JOIN customer_month c2
+    ON c1.customer_id = c2.customer_id
+   AND PERIOD_DIFF(
+        REPLACE(c1.month, '-', ''),
+        REPLACE(c2.month, '-', '')
+   ) = 1
+GROUP BY c1.month
+ORDER BY c1.month;
+
+-- Combined query
+WITH customer_month AS (
+    SELECT DISTINCT
+        customer_id,
+        DATE_FORMAT(rental_date, '%Y-%m') AS month
+    FROM rental
+),
+monthly_active AS (
+    SELECT
+        month,
+        COUNT(customer_id) AS active_customers
+    FROM customer_month
+    GROUP BY month
+),
+retained AS (
+    SELECT
+        c1.month,
+        COUNT(DISTINCT c1.customer_id) AS retained_customers
+    FROM customer_month c1
+    JOIN customer_month c2
+      ON c1.customer_id = c2.customer_id
+     AND PERIOD_DIFF(
+            REPLACE(c1.month, '-', ''),
+            REPLACE(c2.month, '-', '')
+        ) = 1
+    GROUP BY c1.month
+)
+SELECT
+    m.month,
+    m.active_customers,
+    LAG(m.active_customers) OVER (ORDER BY m.month) AS previous_month_active,
+    ROUND(
+        (
+            m.active_customers -
+            LAG(m.active_customers) OVER (ORDER BY m.month)
+        ) * 100.0 /
+        LAG(m.active_customers) OVER (ORDER BY m.month),
+        2
+    ) AS percentage_change,
+    COALESCE(r.retained_customers, 0) AS retained_customers
+FROM monthly_active m
+LEFT JOIN retained r
+    ON m.month = r.month
+ORDER BY m.month;