Lidiia starshynova w2 databases #14

starshynova · 2025-01-08T15:23:39Z

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starshynova · 2025-01-08T15:31:18Z

I tried to implement a more complicated solution for this tasks. But I got some errors that I was not able to solve. This topic is very interesting for me and I would like you to help me with solving my errors.

yunchen4

Hi Lidiia,
It's very good that you're interested in exploring some advanced MySQL syntax and topics! I left some suggestions about real working scenarios related to DB. Feel free to check them.
There's only one point that you need to rework. I have made it explicit.
I saw you left a comment saying you encountered some errors. Don't hesitate to ping me on Slack to share your screenshots and code.
Have a nice weekend!

yunchen4 · 2025-01-10T19:59:46Z

Week2/Assignment/Relationships.js

+const create_table_author_paper_query = `CREATE TABLE IF NOT EXISTS author_paper(
+    author_id INT,
+    paper_id INT,
+    UNIQUE KEY (author_id, paper_id),
+    FOREIGN KEY (author_id) REFERENCES authors(author_id) ON DELETE CASCADE,
+    FOREIGN KEY (paper_id) REFERENCES research_papers(paper_id) ON DELETE CASCADE
+    )`;


Need to work: Defining UNIQUE for the combination of author_id and paper_id is fantastic, but it's strongly recommended to have PK for each table. Why not use it as PK? There is a type of PK called composite key. PK will automatically set the combination to be unique.

yunchen4 · 2025-01-10T20:14:08Z

Week2/Assignment/Relationships.js

+const create_temp_table_query = `CREATE TEMPORARY TABLE temp_author_mentor (author_id INT, mentor_id INT)`;
+
+const insert_mentor_id_into_temp_table_query = `INSERT INTO temp_author_mentor (author_id, mentor_id)
+SELECT author_id, mentor_id
+FROM (
+    SELECT 
+        (SELECT author_id FROM authors WHERE author_name = 'John Doe') AS author_id,
+        (SELECT author_id FROM authors WHERE author_name = 'Alice Green') AS mentor_id
+    UNION ALL
+    SELECT 
+        (SELECT author_id FROM authors WHERE author_name = 'Jane Smith') AS author_id,
+        (SELECT author_id FROM authors WHERE author_name = 'Olivia Brown') AS mentor_id
+    UNION ALL
+    SELECT 
+        (SELECT author_id FROM authors WHERE author_name = 'Alice Green') AS author_id,
+        (SELECT author_id FROM authors WHERE author_name = 'Olivia Brown') AS mentor_id
+    UNION ALL
+    SELECT 
+        (SELECT author_id FROM authors WHERE author_name = 'Michael Brown') AS author_id,
+        (SELECT author_id FROM authors WHERE author_name = 'Jane Smith') AS mentor_id
+    UNION ALL
+    SELECT 
+        (SELECT author_id FROM authors WHERE author_name = 'Robert Black') AS author_id,
+        (SELECT author_id FROM authors WHERE author_name = 'John Doe') AS mentor_id
+    UNION ALL
+    SELECT 
+        (SELECT author_id FROM authors WHERE author_name = 'Sophia Johnson') AS author_id,
+        (SELECT author_id FROM authors WHERE author_name = 'Noah Lee') AS mentor_id
+    UNION ALL
+    SELECT 
+        (SELECT author_id FROM authors WHERE author_name = 'Daniel Martinez') AS author_id,
+        (SELECT author_id FROM authors WHERE author_name = 'Jane Smith') AS mentor_id
+    UNION ALL
+    SELECT 
+        (SELECT author_id FROM authors WHERE author_name = 'Olivia Brown') AS author_id,
+        (SELECT author_id FROM authors WHERE author_name = 'Alice Green') AS mentor_id
+    UNION ALL
+    SELECT 
+        (SELECT author_id FROM authors WHERE author_name = 'Isabella Clark') AS author_id,
+        (SELECT author_id FROM authors WHERE author_name = 'John Doe') AS mentor_id
+    UNION ALL
+    SELECT 
+        (SELECT author_id FROM authors WHERE author_name = 'Mia Hall') AS author_id,
+        (SELECT author_id FROM authors WHERE author_name = 'Sophia Johnson') AS mentor_id
+    UNION ALL
+    SELECT 
+        (SELECT author_id FROM authors WHERE author_name = 'Noah Lee') AS author_id,
+        (SELECT author_id FROM authors WHERE author_name = 'Sophia Johnson') AS mentor_id
+    UNION ALL
+    SELECT 
+        (SELECT author_id FROM authors WHERE author_name = 'Amelia Young') AS author_id,
+        (SELECT author_id FROM authors WHERE author_name = 'Sophia Johnson') AS mentor_id
+    UNION ALL
+    SELECT 
+        (SELECT author_id FROM authors WHERE author_name = 'Sophia Johnson') AS author_id,
+        (SELECT author_id FROM authors WHERE author_name = 'Mia Hall') AS mentor_id
+) AS temp_values`;
+
+const update_mentor_id_query = `
+UPDATE authors AS a1
+JOIN temp_author_mentor AS tam ON a1.author_id = tam.author_id
+SET a1.mentor_id = tam.mentor_id`;


It's good that you want to explore more SQL syntax in this assignment.

In real working situation it's better to avoid over-complicated code (for example UNION ALL and TEMPORARY TABLE). It's hard to read and maintain for long term. I don't see people use TEMPORARY TABLE for backend. I think it's more relevant when you're doing some complex data analysis and want to cache some intermediate data.

yunchen4 · 2025-01-10T20:33:28Z

Week2/Assignment/Relationships.js

+const insert_author_paper_query = `INSERT INTO author_paper (author_id, paper_id) VALUES
+    ((SELECT author_id FROM authors WHERE author_name = 'John Doe'), 
+    (SELECT paper_id FROM research_papers WHERE paper_title = 'Deep Learning Advances')),
+
+    ((SELECT author_id FROM authors WHERE author_name = 'John Doe'), 
+    (SELECT paper_id FROM research_papers WHERE paper_title = 'Quantum Computing Innovations')),
+
+    ((SELECT author_id FROM authors WHERE author_name = 'Jane Smith'), 
+    (SELECT paper_id FROM research_papers WHERE paper_title = 'Blockchain for Supply Chains')),
+
+    ((SELECT author_id FROM authors WHERE author_name = 'Jane Smith'), 
+    (SELECT paper_id FROM research_papers WHERE paper_title = 'Neural Networks in Medicine')),
+
+    ((SELECT author_id FROM authors WHERE author_name = 'Alice Green'), 
+    (SELECT paper_id FROM research_papers WHERE paper_title = 'Climate Change Modeling')),
+
+    ((SELECT author_id FROM authors WHERE author_name = 'Alice Green'), 
+    (SELECT paper_id FROM research_papers WHERE paper_title = 'Advances in Robotics')),
+
+    ((SELECT author_id FROM authors WHERE author_name = 'Michael Brown'), 
+    (SELECT paper_id FROM research_papers WHERE paper_title = 'Ethical AI')),
+
+    ((SELECT author_id FROM authors WHERE author_name = 'Michael Brown'), 
+    (SELECT paper_id FROM research_papers WHERE paper_title = 'Renewable Energy Innovations')),
+
+    ((SELECT author_id FROM authors WHERE author_name = 'Emily White'), 
+    (SELECT paper_id FROM research_papers WHERE paper_title = 'Deep Learning Advances')),
+
+    ((SELECT author_id FROM authors WHERE author_name = 'Emily White'), 
+    (SELECT paper_id FROM research_papers WHERE paper_title = 'Genetic Algorithms in Biology')),
+
+    ((SELECT author_id FROM authors WHERE author_name = 'Robert Black'), 
+    (SELECT paper_id FROM research_papers WHERE paper_title = 'Neural Networks in Medicine')),
+
+    ((SELECT author_id FROM authors WHERE author_name = 'Robert Black'), 
+    (SELECT paper_id FROM research_papers WHERE paper_title = 'Human-Computer Interaction Design')),
+
+    ((SELECT author_id FROM authors WHERE author_name = 'Sophia Johnson'), 
+    (SELECT paper_id FROM research_papers WHERE paper_title = 'Space Exploration and AI')),
+
+    ((SELECT author_id FROM authors WHERE author_name = 'Sophia Johnson'), 
+    (SELECT paper_id FROM research_papers WHERE paper_title = 'Cybersecurity in IoT')),
+
+    ((SELECT author_id FROM authors WHERE author_name = 'Daniel Martinez'), 
+    (SELECT paper_id FROM research_papers WHERE paper_title = 'Machine Learning in Healthcare')),
+
+    ((SELECT author_id FROM authors WHERE author_name = 'Daniel Martinez'), 
+    (SELECT paper_id FROM research_papers WHERE paper_title = 'Deep Learning Advances')),
+
+    ((SELECT author_id FROM authors WHERE author_name = 'Olivia Brown'), 
+    (SELECT paper_id FROM research_papers WHERE paper_title = 'Advances in Cryptography')),
+
+    ((SELECT author_id FROM authors WHERE author_name = 'James Wilson'), 
+    (SELECT paper_id FROM research_papers WHERE paper_title = 'Bioinformatics Tools')),
+
+    ((SELECT author_id FROM authors WHERE author_name = 'Isabella Clark '), 
+    (SELECT paper_id FROM research_papers WHERE paper_title = 'Self-Driving Cars'))`;


It's not recommended to write this kind of code in real working situation. It's hard to read and maintain.

Usually in real work, all mock/test data will be written into a JSON file and then populated into database. Unless you have complex queries, you will use ORM a lot when you're writing backend code, and ORM can help you hide a lot of this complexities.

From my personal experience, in most cases, the most complicated SQL query in real work contains a lot of JOINs or subqueries. Usually when you found yourself are using too many JOINs and subqueries for a single service (queries across multiple services owned by multiple teams, of course, are forgivable), it implies the database schema design might have some problems 😅

yunchen4 · 2025-01-10T20:42:11Z

Week2/Assignment/keys.js

+  university VARCHAR(255),
+  date_of_birth DATE,
+  h_index INT(100),
+  gender VARCHAR(100)


suggestion: gender usually is a set of options: female, male, or undefined. For a set with the finite number of options which hardly changes (gender's definition is pretty stable), we usually use type ENUM.

We can give names for different options in a ENUM, but the value is actually stored as an integer behind the scene. For example, we define ENUM ('M', 'F', 'X'). M is stored as 0 underlying.

yunchen4 · 2025-01-10T20:45:07Z

Week2/Assignment/aggregateFunctions.js

+JOIN authors ON author_paper.author_id = authors.author_id
+WHERE gender = 'Female'`;
+
+const average_h_index_query = `SELECT university AS 'University', ROUND(AVG(h_index), 2) AS 'Average h-index' 


Nice try to use ROUND() 👍

yunchen4 · 2025-01-10T20:53:56Z

Week2/Assignment/aggregateFunctions.js

+await connection.query(use_database_query);
+const [result_all_paper_count_author_query] = await connection.query(all_paper_count_author_query);
+console.log(result_all_paper_count_author_query);
+const [result_research_paper_publishing_woman_query] = await connection.query(research_paper_publishing_woman_query);
+console.log(result_research_paper_publishing_woman_query);
+const [result_average_h_index_query] = await connection.query(average_h_index_query);
+console.log(result_average_h_index_query);
+const [result_sum_papers_university_query] = await connection.query(sum_papers_university_query);
+console.log(result_sum_papers_university_query);
+const [result_min_max_h_index_university_query] = await connection.query(min_max_h_index_university_query);
+console.log(result_min_max_h_index_university_query);


Missing tabs at the beginning. Not a big problem, especially if you use auto formatter

starshynova added 11 commits January 5, 2025 16:17

keys_ready

45ed809

relationships_ver1

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relationships_ver2

ef391d6

keys_fix

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keys_fix2

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relationships_ready

14b999c

keys_fix3

fe19feb

relationships_fix

41d23b1

relationships_fix_mentor_name

8cd79f2

joins+aggregate_function_ready

9751c77

fix_all_error

361e088

yunchen4 self-assigned this Jan 10, 2025

yunchen4 added the To review label Jan 10, 2025

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relationships-fix

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yunchen4 approved these changes Jan 17, 2025

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Lidiia starshynova w2 databases #14

Lidiia starshynova w2 databases #14

starshynova commented Jan 8, 2025

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Lidiia starshynova w2 databases #14

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Lidiia starshynova w2 databases #14

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