PlanetScale Serverless MySQL Patterns

Quick Guide: Use @planetscale/database for edge/serverless MySQL access via HTTP (Fetch API). Use Client to create per-request connections, conn.execute() for parameterized queries, and conn.transaction() for atomic operations. Never run DDL directly on production -- use deploy requests with safe migrations enabled. PlanetScale runs on Vitess: foreign keys are supported but opt-in, stored procedures are not supported, and all schema changes go through online DDL. The built-in cast handles regular integers and floats automatically, but provide a custom cast for BigInt, Date, and boolean columns. Branch your database like git branches for dev/preview environments.

<critical_requirements>

CRITICAL: Before Using This Skill

All code must follow project conventions in CLAUDE.md (kebab-case, named exports, import ordering, import type, named constants)

(You MUST use conn.execute(sql, params) with parameterized queries -- never interpolate user input into SQL strings)

(You MUST use deploy requests for ALL schema changes on production branches with safe migrations enabled -- direct DDL is rejected)

(You MUST create a fresh Client.connection() per request in serverless environments -- do not reuse connections across invocations)

(You MUST handle the Vitess/MySQL compatibility differences: no stored procedures, no RENAME COLUMN via direct DDL, no := operator, no LOAD DATA INFILE)

(You MUST provide a custom cast function for BigInt (INT64/UINT64), Date (DATETIME/TIMESTAMP), and boolean (TINYINT(1)) columns -- the default cast handles regular integers and floats but leaves these as strings)

</critical_requirements>

Auto-detection: PlanetScale, @planetscale/database, planetscale serverless driver, pscale, deploy request, safe migrations, Vitess, database branching, planetscale branch, planetscale boost, mysql serverless, pscale CLI, planetscale connection

When to use:

• Querying MySQL from edge/serverless functions via the PlanetScale serverless driver
• Managing schema changes through deploy requests and safe migrations
• Creating database branches for dev, preview, or CI environments
• Setting up connections with @planetscale/database (host/username/password or URL)
• Running transactions in serverless contexts
• Handling Vitess-specific SQL compatibility constraints
• Programmatic branch management via pscale CLI

Key patterns covered:

• connect() / Client connection setup with host, username, password
• conn.execute() with positional (?) and named (:param) parameters
• conn.transaction() for atomic multi-statement operations
• Custom cast functions for type-safe value conversion (BigInt, Date, boolean)
• Deploy request workflow (branch, change schema, create DR, review, deploy)
• Safe migrations and the no-direct-DDL enforcement model
• Database branching for dev/preview/CI environments
• Vitess SQL compatibility constraints and workarounds
• pscale CLI for branch and deploy request management

When NOT to use:

• Long-running server processes with persistent TCP MySQL connections (use mysql2 driver)
• Complex ORM-specific patterns (use your ORM's own skill)
• General MySQL query syntax (use a SQL/MySQL skill)
• PostgreSQL workloads (use Neon or another Postgres provider)

Detailed Resources:

• For decision frameworks, CLI reference, and quick lookup tables, see reference.md

Driver & Queries:

• examples/core.md -- Connection setup, parameterized queries, transactions, type casting

Branching & Schema Changes:

• examples/branching.md -- Dev branches, deploy requests, safe migrations, pscale CLI, CI/CD workflows

Philosophy

PlanetScale is a serverless MySQL platform built on Vitess, the same technology that powers YouTube's database infrastructure. The @planetscale/database driver uses HTTP (Fetch API) instead of TCP, making MySQL accessible from edge runtimes that lack TCP support.

Core principles:

1. HTTP-based, stateless connections -- Every query is an HTTP request. There are no persistent connections to manage, no connection pools to configure. Create a connection, execute queries, done. PlanetScale handles connection pooling at the infrastructure level (Vitess VTTablet + Global Routing).
2. Schema changes via deploy requests, never direct DDL -- Production branches with safe migrations reject direct CREATE, ALTER, DROP statements. All schema changes go through deploy requests: branch, modify schema on the branch, create a deploy request, review the diff, deploy with zero downtime via online DDL.
3. Branches are cheap -- Database branches are isolated copies of your schema (and optionally data). Create them for feature development, PR previews, CI runs. Delete when done.
4. Vitess under the hood -- PlanetScale runs Vitess, which adds horizontal scaling but introduces SQL compatibility differences. No stored procedures, no RENAME COLUMN in DDL, no := operator. Foreign keys are supported but opt-in and come with performance trade-offs.
5. Default cast handles common types, customize for the rest -- The driver's built-in cast function automatically converts INT8-32 and FLOAT32/64 to JavaScript numbers, and parses JSON. However, INT64/UINT64 (BigInt), DATETIME/TIMESTAMP (Date), DECIMAL, and TINYINT(1) (boolean) remain as strings -- provide a custom cast function for these.

When to use PlanetScale serverless driver:

• Edge/serverless functions that cannot open TCP connections
• Applications using PlanetScale's branching and deploy request workflow
• High-concurrency serverless apps benefiting from PlanetScale's infrastructure-level pooling
• Teams wanting git-like database workflows (branch, review, merge)

When NOT to use:

• Long-running server processes (use mysql2 with TCP for persistent connections)
• Workloads requiring stored procedures, triggers, or events (Vitess does not support them)
• Applications requiring LOAD DATA INFILE (not supported)

Core Patterns

Pattern 1: Connection Setup

The driver provides two connection methods: connect() for a single connection and Client for a connection factory. Use Client in serverless (fresh connection per request), connect() for single long-lived connection objects.

import { connect } from "@planetscale/database";

const conn = connect({
  host: process.env.DATABASE_HOST!,
  username: process.env.DATABASE_USERNAME!,
  password: process.env.DATABASE_PASSWORD!,
});
const { rows } = await conn.execute(
  "SELECT id, name FROM users WHERE active = ?",
  [true],
);

See examples/core.md for full connection patterns including Client factory, URL-based config, and custom fetch for HTTP/2.

Pattern 2: Parameterized Queries

The driver supports positional (?) and named (:param) parameter styles. Both are auto-escaped preventing SQL injection. Never mix styles in a single execute() call.

// Positional: array of values
await conn.execute("SELECT id, name FROM users WHERE id = ? AND active = ?", [
  userId,
  true,
]);

// Named: object of values
await conn.execute("SELECT id, name FROM users WHERE role = :role", {
  role: "admin",
});

See examples/core.md for complex named parameter queries and bad examples to avoid.

Pattern 3: Transactions

conn.transaction() executes multiple queries atomically with automatic rollback on error. Each tx.execute() is an HTTP round trip, but conditional logic runs client-side within the callback.

const result = await conn.transaction(async (tx) => {
  const debit = await tx.execute(
    "UPDATE accounts SET balance = balance - ? WHERE id = ? AND balance >= ?",
    [amount, fromId, amount],
  );
  if (debit.r