D1 Database

D1 is Cloudflare’s serverless SQL database. It’s SQLite at the edge — familiar SQL syntax, zero server management, and it works seamlessly with Workers and Pages.

Why D1?

• SQLite compatible — you already know the syntax
• Serverless — no database servers to manage
• Edge-located — data lives close to your users
• Free tier — 5GB storage, 5M rows read/day, 100K rows written/day
• MCP accessible — Claude can query it directly

Creating a D1 Database

Via Wrangler CLI

npx wrangler d1 create my-app-db

Via Claude with MCP

> Create a new D1 database called "course-db"

Claude uses the Cloudflare MCP to create it directly.

Schema Design with Claude

> Create a D1 schema for a simple blog:
> - posts (id, title, slug, content, published_at, status)
> - tags (id, name, slug)
> - post_tags (post_id, tag_id)

Claude generates the migration:

-- migrations/0001_initial.sql
CREATE TABLE posts (
  id INTEGER PRIMARY KEY AUTOINCREMENT,
  title TEXT NOT NULL,
  slug TEXT NOT NULL UNIQUE,
  content TEXT NOT NULL,
  published_at TEXT,
  status TEXT NOT NULL DEFAULT 'draft',
  created_at TEXT NOT NULL DEFAULT (datetime('now')),
  updated_at TEXT NOT NULL DEFAULT (datetime('now'))
);

CREATE TABLE tags (
  id INTEGER PRIMARY KEY AUTOINCREMENT,
  name TEXT NOT NULL,
  slug TEXT NOT NULL UNIQUE
);

CREATE TABLE post_tags (
  post_id INTEGER NOT NULL REFERENCES posts(id) ON DELETE CASCADE,
  tag_id INTEGER NOT NULL REFERENCES tags(id) ON DELETE CASCADE,
  PRIMARY KEY (post_id, tag_id)
);

CREATE INDEX idx_posts_slug ON posts(slug);
CREATE INDEX idx_posts_status ON posts(status);
CREATE INDEX idx_tags_slug ON tags(slug);

Run the migration

npx wrangler d1 execute my-app-db --file=migrations/0001_initial.sql

Querying D1 from Workers

export default {
  async fetch(request: Request, env: Env): Promise<Response> {
    const posts = await env.DB.prepare(
      'SELECT * FROM posts WHERE status = ? ORDER BY published_at DESC LIMIT ?'
    ).bind('published', 10).all();

    return Response.json(posts.results);
  },
};

Querying D1 via MCP

With the Cloudflare MCP server, Claude can query your D1 databases directly:

> Query the course-db D1 database:
> SELECT COUNT(*) as total, status FROM posts GROUP BY status

This is incredibly useful for:

• Checking data during development
• Debugging production issues
• Generating reports

Exercise

1. Create a D1 database
2. Ask Claude to design a schema for your use case
3. Run the migration
4. Create a Worker that reads from D1
5. Use the Cloudflare MCP to query the database directly