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Node.js - PostgreSQL HAVING clause

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Created by:

Geospatial-Palus

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In this article, we would like to show you how to use PostgreSQL HAVING clause in Node.js.

Example data used with GROUP BY statement - HeidiSQL — Example data used with HAVING clause - HeidiSQL

Note: at the end of this article you can find database preparation SQL queries.

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const { Client } = require('pg');
​
const client = new Client({
    host: '127.0.0.1',
    user: 'postgres',
    database: 'database_name',
    password: 'password',
    port: 5432,
});
​
const fetchGroupedUsers = async (minimum) => {
    const query = `SELECT COUNT("id") AS "number of users", "country"
                   FROM "users"
                   GROUP BY "country"
                   HAVING COUNT("id") >= $1;`;
    try {
        await client.connect();  // creates connection
        const { rows } = await client.query(query, [minimum]); // sends query
        console.table(rows);
    } catch (error) {
        console.error(error.stack);
    } finally {
        await client.end();      // closes connection
    }
};
​
fetchGroupedUsers(2); // Each group will have at least 2 users.

Result:

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┌─────────┬─────────────────┬───────────┐
│ (index) │ number of users │  country  │
├─────────┼─────────────────┼───────────┤
│    0    │       '3'       │  'Spain'  │
│    1    │       '2'       │ 'Vietnam' │
└─────────┴─────────────────┴───────────┘

Database preparation

Edit

create_tables.sql file:

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CREATE TABLE "users" (
    "id" SERIAL,
    "name" VARCHAR(100) NOT NULL,
    "country" VARCHAR(15) NOT NULL,
    PRIMARY KEY ("id")
);

insert_data.sql file:

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INSERT INTO "users"
    ("name", "country")
VALUES
    ('Tom', 'Poland'),
    ('Chris', 'Spain'),
    ('Jack', 'Spain'),
    ('Kim', 'Vietnam'),
    ('Marco', 'Italy'),
    ('Kate', 'Spain'),
    ('Nam', 'Vietnam');