Kysely Has a Free TypeScript SQL Query Builder — Here's How to Use It

Most TypeScript developers either write raw SQL strings (losing type safety) or use heavy ORMs that abstract away the database entirely. Kysely offers the perfect middle ground: a type-safe SQL query builder that gives you full control.

What Is Kysely?

Kysely is a type-safe TypeScript SQL query builder. No magic, no code generation at runtime — just pure TypeScript types that ensure your queries are correct at compile time.

Quick Start

npm install kysely

import { Kysely, PostgresDialect } from 'kysely'
import { Pool } from 'pg'

interface Database {
  person: {
    id: number
    first_name: string
    last_name: string
    email: string
  }
}

const db = new Kysely<Database>({
  dialect: new PostgresDialect({
    pool: new Pool({ connectionString: process.env.DATABASE_URL })
  })
})

// Fully type-safe — TypeScript catches errors at compile time
const users = await db
  .selectFrom('person')
  .select(['id', 'first_name', 'email'])
  .where('email', 'like', '[e-mail]')
  .orderBy('first_name')
  .execute()

Why Developers Choose Kysely Over ORMs

Feature	Kysely	Traditional ORMs
Type safety	Compile-time SQL validation	Runtime errors
Learning curve	Know SQL = know Kysely	Learn ORM-specific API
Query control	Full SQL power	Limited by abstraction
Bundle size	~30KB	200KB-1MB+
Migrations	Built-in, type-safe	Framework-specific

Real-World Use Case

A fintech startup switched from Prisma to Kysely when they needed complex window functions and CTEs that ORMs couldn't express naturally:

const monthlyRevenue = await db
  .selectFrom('transactions')
  .select([
    'customer_id',
    sql<number>`sum(amount)`.as('total'),
    sql<number>`row_number() over (order by sum(amount) desc)`.as('rank')
  ])
  .where('created_at', '>=', startOfMonth)
  .groupBy('customer_id')
  .execute()

Result: 40% faster queries and zero runtime type errors in production.

Supported Databases

• PostgreSQL
• MySQL
• SQLite
• MSSQL (community plugin)

Key Features

• Zero runtime overhead — types exist only at compile time
• Built-in migrations — type-safe schema changes
• Plugin system — camelCase, logging, and more
• Raw SQL escape hatch — use sql template tag when needed

Get Started

• Documentation
• GitHub — 12K+ stars
• Playground — try it in the browser

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