DMYTRO_DORONIN-w4-database

Week2/assignment/aggregates.js

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+import { client } from './db.js'
+
+const papersWithAuthorsCount = `
+    SELECT
+        rp.paper_id,
+        rp.paper_title,
+        COUNT(ap.author_id) AS authors_count
+    FROM research_papers rp
+    LEFT JOIN authors_papers ap
+        ON rp.paper_id = ap.paper_id
+    GROUP BY rp.paper_id, rp.paper_title
+    ORDER BY rp.paper_id
+`
+
+const totalPapersByFemaleAuthors = `
+    SELECT
+        COUNT(DISTINCT ap.paper_id) AS total_papers_by_female_authors
+    FROM authors a
+    JOIN authors_papers ap
+        ON a.author_id = ap.author_id
+    WHERE a.gender = 'female'
+`
+
+const avgHIndexPerUniversity = `
+    SELECT
+        university,
+        AVG(h_index) AS avg_h_index
+    FROM authors
+    GROUP BY university
+    ORDER BY university
+`
+
+const totalPapersPerUniversity = `
+    SELECT
+        a.university,
+        COUNT(DISTINCT ap.paper_id) AS total_papers
+    FROM authors a
+    LEFT JOIN authors_papers ap
+        ON a.author_id = ap.author_id
+    GROUP BY a.university
+    ORDER BY a.university
+`
+
+const minMaxHIndexPerUniversity = `
+    SELECT
+        university,
+        MIN(h_index) AS min_h_index,
+        MAX(h_index) AS max_h_index
+    FROM authors
+    GROUP BY university
+    ORDER BY university
+`
+
+async function main() {
+    try {
+        await client.connect()
+        console.log('Connected to DB')
+
+        const res1 = await client.query(papersWithAuthorsCount)
+        console.table(res1.rows)
+
+        const res2 = await client.query(totalPapersByFemaleAuthors)
+        console.table(res2.rows)
+
+        const res3 = await client.query(avgHIndexPerUniversity)
+        console.table(res3.rows)
+
+        const res4 = await client.query(totalPapersPerUniversity)
+        console.table(res4.rows)
+
+        const res5 = await client.query(minMaxHIndexPerUniversity)
+        console.table(res5.rows)
+    } catch (err) {
+        console.error('Error in exercise4_aggregates:', err)
+    } finally {
+        await client.end()
+        console.log('Connection closed')
+    }
+}
+
+main()

Week2/assignment/db.js

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+import pg from 'pg'
+
+export const client = new pg.Client({
+    user: 'postgres',
+    host: 'localhost',
+    database: 'postgres',
+    password: '123456',
+    port: 5432,
+})

Week2/assignment/joins.js

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+import { client } from './db.js'
+
+const queryAuthorsWithMentors = `
+    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 queryAuthorsWithPapers = `
+    SELECT
+        a.author_id,
+        a.author_name,
+        a.university,
+        a.date_of_birth,
+        a.h_index,
+        a.gender,
+        rp.paper_title
+    FROM authors a
+    LEFT JOIN authors_papers ap
+        ON ap.author_id = a.author_id
+    LEFT JOIN research_papers rp
+        ON rp.paper_id = ap.paper_id
+    ORDER BY a.author_id, rp.paper_title
+`
+
+async function main() {
+    try {
+        await client.connect()
+        console.log('Connected to DB')
+
+        const res1 = await client.query(queryAuthorsWithMentors)
+        console.table(res1.rows)
+
+        const res2 = await client.query(queryAuthorsWithPapers)
+        console.table(res2.rows)
+    } catch (err) {
+        console.error('Error in exercise3_joins:', err)
+    } finally {
+        await client.end()
+        console.log('Connection closed')
+    }
+}
+
+main()

Week2/assignment/keys.js

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+import { client } from './db.js'
+
+const createAuthorsTable = `
+    CREATE TABLE IF NOT EXISTS authors (
+        author_id     SERIAL PRIMARY KEY,
+        author_name   TEXT NOT NULL,
+        university    TEXT,
+        date_of_birth DATE,
+        h_index       INTEGER,
+        gender        VARCHAR(10)
+        )
+`
+
+const addMentorColumn = `
+    ALTER TABLE authors
+        ADD COLUMN IF NOT EXISTS mentor INTEGER
+`
+
+const addMentorForeignKey = `
+    DO $$
+    BEGIN
+        IF NOT EXISTS (
+            SELECT 1
+            FROM information_schema.table_constraints
+            WHERE constraint_name = 'fk_authors_mentor'
+            AND table_name = 'authors'
+        ) THEN
+            ALTER TABLE authors
+            ADD CONSTRAINT fk_authors_mentor
+            FOREIGN KEY (mentor)
+            REFERENCES authors(author_id)
+            ON DELETE SET NULL
+        END IF
+    END
+    $$
+`
+
+async function main() {
+    try {
+        await client.connect()
+        console.log('Connected to DB')
+
+        await client.query(createAuthorsTable)
+
+        await client.query(addMentorColumn)
+
+        await client.query(addMentorForeignKey)
+    } catch (err) {
+        console.error('Error in exercise1_keys:', err)
+    } finally {
+        await client.end()
+        console.log('Connection closed')
+    }
+}
+
+main()

Week2/assignment/package.json

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