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>

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)

</philosophy>

---

<patterns>

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.rowsAffected === 0) throw new Error("Insufficient funds"); // triggers rollback
  await tx.execute("UPDATE accounts SET balance = balance + ? WHERE id = ?", [
    amount,
    toId,
  ]);
  return debit;
});

See examples/core.md for full transaction examples with inventory checks and FOR UPDATE locking.

---

Pattern 4: Custom Type Casting

The built-in cast handles INT8-32 and FLOAT32/64 automatically. Provide a custom cast for INT64/UINT64 (BigInt), DATETIME/TIMESTAMP (Date), and TINYINT(1) (boolean) -- these remain as strings by default.

import { connect, cast } from "@planetscale/database";
import type { Field } from "@planetscale/database";

function customCast(field: Field, value: any): any {
  if (value == null) return null;
  if (field.type === "INT64" || field.type === "UINT64") return BigInt(value);
  if (field.type === "DATETIME" || field.type === "TIMESTAMP")
    return new Date(value + "Z");
  if (field.type === "INT8" && field.columnLength === 1) return value === "1";
  return cast(field, value);
}

const conn = connect({ url: process.env.DATABASE_URL, cast: customCast });

See examples/core.md for per-query cast overrides and type-specific cast variants.

---

Pattern 5: Deploy Request Workflow

Schema changes on production branches with safe migrations must go through deploy requests. Direct DDL is rejected. The workflow is: branch, modify schema, create deploy request, review diff, deploy.

pscale branch create my-database add-user-roles          # 1. Create dev branch
pscale shell my-database add-user-roles                  # 2. Make schema changes (DDL)
pscale deploy-request create my-database add-user-roles --into main  # 3. Create DR
pscale deploy-request diff my-database 1                 # 4. Review schema diff
pscale deploy-request deploy my-database 1               # 5. Deploy (online DDL)
pscale deploy-request revert my-database 1               # 6. Revert within 30 min if needed

See examples/branching.md for gated deployments, instant deployments, and CI/CD workflows.

---

Pattern 6: Database Branching

Branches are isolated copies of your database schema. Development branches allow direct DDL. Production branches require deploy requests when safe migrations is enabled.

pscale branch create my-database dev-alice               # Create dev branch
pscale shell my-database dev-alice                       # Interactive MySQL shell
pscale password create my-database dev-alice my-password # Generate app credentials
pscale branch delete my-database dev-alice               # Clean up when done

See examples/branching.md for PR preview branches, safe column renames, FK setup, and branch cleanup scripts.

---

Pattern 7: Vitess SQL Compatibility

PlanetScale runs on Vitess, which introduces SQL differences from standard MySQL. Key constraints: no stored procedures/triggers/events, no RENAME COLUMN (use three-step add/migrate/drop pattern), no := operator, no LOAD DATA INFILE, no CREATE DATABASE.

See reference.md for the full supported/unsupported SQL compatibility table.

</patterns>

---

<decision_framework>

Decision Framework

Connection Method

What is the runtime environment?
+-- Edge/serverless (Cloudflare Workers, Vercel Edge, etc.)
|   +-- Use @planetscale/database (HTTP-based, no TCP needed)
+-- Traditional Node.js server (always-on)
|   +-- Need PlanetScale branching/deploy workflow?
|   |   +-- YES --> @planetscale/database works fine (HTTP)
|   |   +-- NO --> mysql2 driver with TCP may be simpler
+-- ORM integration?
    +-- Check your ORM's docs for its PlanetScale/serverless adapter

connect() vs Client

How many connections per process?
+-- Single connection (scripts, simple handlers) --> connect()
+-- Multiple connections (serverless, per-request) --> Client + client.connection()

Schema Change Strategy

Is the target branch a production branch with safe migrations?
+-- YES --> Deploy requests ONLY (direct DDL is rejected)
|   +-- Simple change (add column, add index) --> Standard deploy request
|   +-- Needs controlled cutover timing --> Gated deployment (--disable-auto-apply)
|   +-- Instant-eligible change --> Deploy with --instant flag
+-- NO (development branch) --> Direct DDL is allowed
    +-- Experimenting --> pscale shell <db> <branch>
    +-- Scripted migration --> Connect to branch, run DDL

Foreign Keys

Do you need foreign key constraints?
+-- YES --> Enable in database settings (opt-in)
|   +-- Aware of limitations?
|   |   +-- Deploy requests don't validate existing referential integrity
|   |   +-- Reverts can create orphaned rows
|   |   +-- Performance impact in high-concurrency workloads
|   +-- Sharded database? --> FK only supported on unsharded databases
+-- NO --> Use application-level referential integrity
    +-- ORM-level relationship definitions
    +-- Application validation before INSERT/DELETE

</decision_framework>

---

<red_flags>

RED FLAGS

High Priority Issues:

• String interpolation in SQL -- conn.execute(\SELECT * FROM users WHERE id = '${id}'`)bypasses parameterization. Always use?or:param` placeholders with the params argument.
• Direct DDL on production with safe migrations -- ALTER TABLE statements are silently rejected on production branches with safe migrations enabled. All schema changes must go through deploy requests.
• No custom cast for BigInt/Date columns -- The default cast handles regular integers and floats, but INT64/UINT64 remain as strings and DATETIME/TIMESTAMP are not converted to Date objects. Provide a custom cast for these types.

Medium Priority Issues:

• Reusing connections across serverless invocations -- Each serverless invocation gets a fresh execution context. Do not store connection state in global variables expecting it to persist.
• Using RENAME COLUMN in deploy requests -- Column renames can be destructive through Vitess online DDL. Use the three-step pattern: add new column, migrate data, drop old column.
• Missing revert window awareness -- Deploy requests can be reverted within 30 minutes. After that window closes, you must create a new deploy request to undo changes. Plan accordingly.
• Foreign keys enabled without understanding implications -- FK constraints on PlanetScale don't validate existing referential integrity during ALTER TABLE ADD FOREIGN KEY. Orphaned rows will silently remain.

Common Mistakes:

• Wrong package name -- The package is @planetscale/database, not planetscale, mysql-planetscale, or @planetscale/serverless.
• Expecting connection pooling in the driver -- @planetscale/database does not do client-side connection pooling. PlanetScale handles pooling at the infrastructure level (Vitess VTTablet + Global Routing). Do not wrap it in a pool library.
• Using positional and named params together -- A single execute() call uses either ? with an array OR :param with an object. Never mix them.
• Expecting Node.js mysql2 compatibility -- @planetscale/database has a different API from mysql2. There is no pool.query(), no connection.query(). The API is conn.execute(sql, params).
• Running CREATE DATABASE or DROP DATABASE -- Database creation/deletion is managed via the PlanetScale dashboard, API, or pscale CLI, not SQL.

Gotchas & Edge Cases:

• INT64/UINT64 and dates remain as strings with the default cast -- SELECT count(*) as total returns { total: 42 } (INT64 is an exception -- it stays as "42" string). DATETIME returns "2024-01-15 10:30:00". Regular INT32 and FLOAT types are auto-converted.
• rowsAffected is 0 for SELECT -- Only DML statements (INSERT, UPDATE, DELETE) populate rowsAffected. For SELECT, check rows.length or size.
• insertId is a string -- Even though MySQL auto-increment IDs are integers, insertId in the result is always a string. Cast if needed: BigInt(result.insertId).
• Transactions over HTTP are not interactive -- Unlike traditional MySQL transactions, PlanetScale's HTTP transactions send all statements in a single request. You CAN use conditional logic within the transaction() callback (it runs client-side), but each tx.execute() is an HTTP round trip.
• DATETIME values lack timezone -- MySQL DATETIME is stored without timezone info. The driver returns it as a string like "2024-01-15 10:30:00". Append "Z" when parsing as UTC, or handle timezone explicitly.
• 64KB query limit per execute -- Individual SQL statements have a size limit. For bulk inserts, batch into multiple execute() calls.
• SQL mode is session-only -- SET sql_mode = '...' only lasts for the current connection. On PlanetScale's HTTP driver, that means a single request. Global SQL mode changes are not allowed.
• PlanetScale Boost requires explicit opt-in -- Boost query caching is available on Scaler Pro plans and above. Enable per-query via @@boost_cached_queries = true in a session SET before the boosted query. Not all queries are eligible.
• Empty schemas are invalid -- Production branches require at least one table. You cannot have an empty database on a production branch.
• Instant deployments cannot be reverted -- Using --instant on a deploy request uses MySQL's ALGORITHM=INSTANT and skips the revert window entirely.

</red_flags>

---

<critical_reminders>

CRITICAL REMINDERS

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)

Failure to follow these rules will cause SQL injection vulnerabilities, failed deploy requests, or silent type coercion bugs.

</critical_reminders>