Node.js MySQL and PostgreSQL

What is MySQL and PostgreSQL in Node.js?

Node connects to relational databases through driver packages — mysql2 for MySQL and pg for PostgreSQL. Both support connection pooling and parameterised queries, which are essential for performance and safety.

MySQL and PostgreSQL example

import mysql from 'mysql2/promise';

const pool = mysql.createPool({
  host: process.env.DB_HOST,
  user: process.env.DB_USER,
  password: process.env.DB_PASSWORD,
  database: 'jobs',
  connectionLimit: 10,
});

// parameterised — the ONLY safe way to include user input
const [rows] = await pool.execute(
  'SELECT id, title FROM jobs WHERE city = ? AND status = ? LIMIT ?',
  [city, 'active', 20]
);

// PostgreSQL uses $1, $2 placeholders
const { rows } = await pgPool.query(
  'SELECT id, title FROM jobs WHERE city = $1 LIMIT $2',
  [city, 20]
);

Key points to remember

• Create one pool at startup and reuse it — never one connection per request.
• Always parameterise; string concatenation is SQL injection.
• Use a transaction when several writes must succeed or fail together.
• Prisma, Drizzle, Knex and Sequelize add query building and migrations on top.

Common mistakes with MySQL and PostgreSQL

• Building SQL with template literals containing user input.
• Opening a connection per request and exhausting the database’s connection limit.
• Forgetting to release a connection taken from the pool for a transaction.