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Node.js - PostgreSQL SELECT DISTINCT statement

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Created by:

Richard-Bevan

413

In this article, we would like to show you how to make PostgreSQL SELECT DISTINCT statement in Node.js.

example data used with SELECT DISTINCT statement — Example data used with SELECT DISTINCT statement - HeidiSQL

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

1. Practical example

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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 fetchUniqueUsers = async () => {
    try {
        await client.connect();      // gets connection
        const { rows } = await client.query('SELECT DISTINCT "country" FROM "users"');
        console.table(rows);
    } catch (error) {
        console.error(error.stack);
    } finally {
        await client.end();          // closes connection
    }
};
​
fetchUniqueUsers();

Result:

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

2. Database preparation

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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');