Node.js - PostgreSQL - count distinct values

In this article, we would like to show you how to count distinct values in the PostgreSQL database using Node.js.

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

const { Client } = require('pg');

const client = new Client({
    host: '127.0.0.1',
    user: 'postgres',
    database: 'database_name',
    password: 'password',
    port: 5432,
});

const countUniqueCountries = async () => {
    const query = `SELECT COUNT(DISTINCT("country")) AS "unique_countries"
                   FROM "users";`;
    try {
        await client.connect();  // creates connection
        const { rows } = await client.query(query); // sends query
        console.log(rows);
    } catch (error) {
        console.error(error.stack);
    } finally {
        await client.end();      // closes connection
    }
};

countUniqueCountries();

Result: 

[ { unique_countries: '4' } ]

Database preparation

create_tables.sql file:

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

insert_data.sql file:

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