sql challenge on joins

Author: mayankSystems

src/main/java/dev/mayankg/db_concepts/mysql/exc04/joins_challenge2.sql

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+-- Select the current database
+SELECT DATABASE();
+
+-- Show all databases
+SHOW DATABASES;
+
+-- Switch to the 'challenges' database
+USE challenges;
+
+-- Show all tables in the current database
+SHOW TABLES;
+
+-- Select all data from the 'reviewers' table
+SELECT * FROM reviewers;
+
+-- Select all data from the 'series' table
+SELECT * FROM series;
+
+-- Select all data from the 'reviews' table
+SELECT * FROM reviews;
+
+-- Join 'series' and 'reviews' to get series title and corresponding ratings
+SELECT s.title, r.rating
+FROM series s
+JOIN reviews r ON s.id = r.series_id;
+
+-- Get average rating per series, ordered by lowest to highest average rating
+SELECT s.title, ROUND(AVG(r.rating), 2) AS avg_rating
+FROM series s
+JOIN reviews r ON s.id = r.series_id
+GROUP BY s.title
+ORDER BY avg_rating ASC;
+
+-- Join reviewers with their reviews
+SELECT r.first_name, r.last_name, r2.rating
+FROM reviewers r
+INNER JOIN reviews r2 ON r.id = r2.reviewer_id;
+
+-- Find series that have not received any reviews
+SELECT s.title AS unreviewed_series
+FROM series s
+LEFT JOIN reviews r ON s.id = r.series_id
+WHERE r.rating IS NULL;
+
+-- Get average rating per genre, sorted by average
+SELECT s.genre, ROUND(AVG(r.rating), 2) AS avg_rating
+FROM series s
+JOIN reviews r ON s.id = r.series_id
+GROUP BY s.genre
+ORDER BY avg_rating;
+
+-- Reviewer summary: total ratings, min, max, avg rating, and activity status
+SELECT
+    r1.first_name,
+    r1.last_name,
+    COUNT(r2.rating) AS number_ratings,
+    IFNULL(MIN(r2.rating), 0) AS min_rating,
+    IFNULL(MAX(r2.rating), 0) AS max_rating,
+    IFNULL(ROUND(AVG(r2.rating), 2), 0) AS avg_rating,
+    CASE
+        WHEN IFNULL(MIN(r2.rating), 0) = 0 THEN 'INACTIVE'
+        ELSE 'ACTIVE'
+    END AS status
+FROM reviewers r1
+LEFT JOIN reviews r2 ON r1.id = r2.reviewer_id
+GROUP BY r1.first_name, r1.last_name
+ORDER BY r1.first_name, r1.last_name ASC;
+
+-- Get all reviews with series title and reviewer name
+SELECT
+    s.title,
+    r1.rating,
+    CONCAT(r2.first_name, ' ', r2.last_name)
+FROM reviews r1
+INNER JOIN series s ON s.id = r1.series_id
+INNER JOIN reviewers r2 ON r1.reviewer_id = r2.id;

src/main/java/dev/mayankg/db_concepts/mysql/exc04/starter_data.sql

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+select database();
+show databases;
+use challenges;
+
+-- Create a database named 'challenges'
+CREATE TABLE reviewers (
+    id INT PRIMARY KEY AUTO_INCREMENT,
+    first_name VARCHAR(20) NOT NULL,
+    last_name VARCHAR(20) NOT NULL
+);
+
+-- Create a table named 'series' with columns for id, title, released_year, and genre
+CREATE TABLE series (
+    id INT PRIMARY KEY AUTO_INCREMENT,
+    title VARCHAR(50),
+    released_year YEAR,
+    genre VARCHAR(20)
+);
+
+-- Create a table named 'reviews' with columns for id, rating, series_id, and reviewer_id
+CREATE TABLE reviews (
+    id INT PRIMARY KEY AUTO_INCREMENT,
+    rating DECIMAL(2 , 1),
+    series_id INT,
+    reviewer_id INT,
+    FOREIGN KEY (series_id) REFERENCES series (id),
+    FOREIGN KEY (reviewer_id) REFERENCES reviewers (id)
+);
+
+show tables;
+
+-- Insert sample data into the 'series' table
+INSERT INTO series (title, released_year, genre) VALUES
+    ('Archer', 2009, 'Animation'),
+    ('Arrested Development', 2003, 'Comedy'),
+    ("Bob's Burgers", 2011, 'Animation'),
+    ('Bojack Horseman', 2014, 'Animation'),
+    ("Breaking Bad", 2008, 'Drama'),
+    ('Curb Your Enthusiasm', 2000, 'Comedy'),
+    ("Fargo", 2014, 'Drama'),
+    ('Freaks and Geeks', 1999, 'Comedy'),
+    ('General Hospital', 1963, 'Drama'),
+    ('Halt and Catch Fire', 2014, 'Drama'),
+    ('Malcolm In The Middle', 2000, 'Comedy'),
+    ('Pushing Daisies', 2007, 'Comedy'),
+    ('Seinfeld', 1989, 'Comedy'),
+    ('Stranger Things', 2016, 'Drama');
+
+
+INSERT INTO reviewers (first_name, last_name) VALUES
+    ('Thomas', 'Stoneman'),
+    ('Wyatt', 'Skaggs'),
+    ('Kimbra', 'Masters'),
+    ('Domingo', 'Cortes'),
+    ('Colt', 'Steele'),
+    ('Pinkie', 'Petit'),
+    ('Marlon', 'Crafford');
+
+
+INSERT INTO reviews(series_id, reviewer_id, rating) VALUES
+    (1,1,8.0),(1,2,7.5),(1,3,8.5),(1,4,7.7),(1,5,8.9),
+    (2,1,8.1),(2,4,6.0),(2,3,8.0),(2,6,8.4),(2,5,9.9),
+    (3,1,7.0),(3,6,7.5),(3,4,8.0),(3,3,7.1),(3,5,8.0),
+    (4,1,7.5),(4,3,7.8),(4,4,8.3),(4,2,7.6),(4,5,8.5),
+    (5,1,9.5),(5,3,9.0),(5,4,9.1),(5,2,9.3),(5,5,9.9),
+    (6,2,6.5),(6,3,7.8),(6,4,8.8),(6,2,8.4),(6,5,9.1),
+    (7,2,9.1),(7,5,9.7),
+    (8,4,8.5),(8,2,7.8),(8,6,8.8),(8,5,9.3),
+    (9,2,5.5),(9,3,6.8),(9,4,5.8),(9,6,4.3),(9,5,4.5),
+    (10,5,9.9),
+    (13,3,8.0),(13,4,7.2),
+    (14,2,8.5),(14,3,8.9),(14,4,8.9);