DARYNA-TKACHENKO-W2-DATABASE

Week2/assigments/ aggregateFunctions.js

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+import { client } from './database.js';
+
+async function exercise4Aggregates() {
+    try {
+        await client.connect();
+
+
+        const papersCountQuery = `
+            SELECT rp.paper_title,
+                   COUNT(ap.author_id) AS author_count
+            FROM research_papers rp
+            LEFT JOIN author_paper ap
+                   ON rp.paper_id = ap.paper_id
+            GROUP BY rp.paper_title
+            ORDER BY rp.paper_title;
+        `;
+        const papersCountResult = await client.query(papersCountQuery);
+        console.table(papersCountResult.rows);
+
+
+        const femalePapersQuery = `
+            SELECT COUNT(ap.paper_id) AS total_papers_by_female_authors
+            FROM authors a
+            JOIN author_paper ap
+                  ON a.author_id = ap.author_id
+            WHERE a.gender = 'Female';
+        `;
+        const femalePapersResult = await client.query(femalePapersQuery);
+        console.table(femalePapersResult.rows);
+
+
+        const avgHIndexQuery = `
+            SELECT university,
+                   AVG(h_index) AS avg_h_index
+            FROM authors
+            GROUP BY university
+            ORDER BY university;
+        `;
+        const avgHIndexResult = await client.query(avgHIndexQuery);
+        console.table(avgHIndexResult.rows);
+
+
+        const papersByUniversityQuery = `
+            SELECT a.university,
+                   COUNT(ap.paper_id) AS total_papers
+            FROM authors a
+            LEFT JOIN author_paper ap
+                   ON a.author_id = ap.author_id
+            GROUP BY a.university
+            ORDER BY a.university;
+        `;
+        const papersByUniversityResult = await client.query(papersByUniversityQuery);
+        console.table(papersByUniversityResult.rows);
+
+
+        const hIndexMinMaxQuery = `
+            SELECT university,
+                   MIN(h_index) AS min_h_index,
+                   MAX(h_index) AS max_h_index
+            FROM authors
+            GROUP BY university
+            ORDER BY university;
+        `;
+
+        const hIndexMinMaxResult = await client.query(hIndexMinMaxQuery);
+        console.table(hIndexMinMaxResult.rows);
+
+    } catch (error) {
+        console.error("Error:", error);
+    } finally {
+        await client.end();
+    }
+}
+
+exercise4Aggregates();

Week2/assigments/database.js

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+import pkg from 'pg';
+const { Client } = pkg;
+
+export const client = new Client({
+    user: 'hyfuser',
+    host: 'localhost',
+    database: 'authors_db',
+    password: 'hyfpassword',
+    port: 5432,
+});

Week2/assigments/joins.js

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+import { client } from './database.js';
+
+async function exercise3Joins() {
+    try {
+        await client.connect();
+
+        const mentorQuery = `
+            SELECT a.author_name AS author,
+                   m.author_name AS mentor
+            FROM authors a
+                     LEFT JOIN authors m
+                               ON a.mentor = m.author_id
+            ORDER BY a.author_id;
+        `;
+        const mentorResult = await client.query(mentorQuery);
+        console.log("Authors and their mentors:");
+        console.table(mentorResult.rows);
+
+        const papersQuery = `
+            SELECT a.author_id,
+                   a.author_name,
+                   a.university,
+                   a.date_of_birth,
+                   a.h_index,
+                   a.gender,
+                   a.mentor,
+                   rp.paper_title
+            FROM authors a
+                     LEFT JOIN author_paper ap
+                               ON a.author_id = ap.author_id
+                     LEFT JOIN research_papers rp
+                               ON ap.paper_id = rp.paper_id
+            ORDER BY a.author_id, rp.paper_id;
+        `;
+
+        const papersResult = await client.query(papersQuery);
+        console.log("Authors and their papers:");
+        console.table(papersResult.rows);
+
+    } catch (error) {
+        console.error("Error:", error);
+    } finally {
+        await client.end();
+    }
+}
+
+exercise3Joins();

Week2/assigments/key.js

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+import { client } from './database.js'
+
+async function setupAuthorsTable() {
+    try {
+        await client.connect();
+
+        const sql = `
+            DROP TABLE IF EXISTS author_paper CASCADE;
+            DROP TABLE IF EXISTS research_papers CASCADE;
+            DROP TABLE IF EXISTS authors CASCADE;
+
+            CREATE TABLE authors
+            (
+                author_id     SERIAL PRIMARY KEY,
+                author_name   VARCHAR(255),
+                university    VARCHAR(255),
+                date_of_birth DATE,
+                h_index       INT,
+                gender        VARCHAR(10)
+            );
+
+            ALTER TABLE authors
+                ADD COLUMN mentor INT;
+
+            ALTER TABLE authors
+                ADD CONSTRAINT fk_mentor
+                    FOREIGN KEY (mentor)
+                        REFERENCES authors (author_id)
+                        ON DELETE SET NULL;
+        `;
+
+        await client.query(sql);
+        console.log('Authors table created');
+    } catch (err) {
+        console.error('Problem creating authors table', err);
+    } finally {
+        await client.end();
+    }
+}
+
+setupAuthorsTable();

Week2/assigments/package.json

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+{
+  "name": "assigments",
+  "type": "module",
+  "version": "1.0.0",
+  "description": "",
+  "main": "database.js",
+  "scripts": {
+    "test": "echo \"Error: no test specified\" && exit 1"
+  },
+  "keywords": [],
+  "author": "",
+  "license": "ISC",
+  "dependencies": {
+    "pg": "^8.16.3"
+  }
+}