Claude Code: MCP（Model Context Protocol）

# 无 MCP：手动查数据库
> 帮我看看 users 表有多少条记录
Claude Code: 我无法直接访问数据库。你可以运行：
  psql -c "SELECT COUNT(*) FROM users"

# 有 MCP（PostgreSQL Server）：直接查询
> 帮我看看 users 表有多少条记录
Claude Code: [通过 PostgreSQL MCP 查询]
  users 表有 12,450 条记录。
  其中活跃用户 8,920（71.6%），
  最近 7 天注册 342 人。

// ~/.claude/mcp_settings.json
{
  "mcpServers": {
    "filesystem": {
      "command": "npx",
      "args": ["-y", "@anthropic/mcp-filesystem", "/home/user/projects"],
      "env": {}
    },
    "postgres": {
      "command": "npx",
      "args": ["-y", "@anthropic/mcp-postgres"],
      "env": {
        "DATABASE_URL": "postgresql://user:pass@localhost:5432/mydb"
      }
    }
  }
}

// .claude/mcp_settings.json
{
  "mcpServers": {
    "github": {
      "command": "npx",
      "args": ["-y", "@anthropic/mcp-github"],
      "env": {
        "GITHUB_TOKEN": "ghp_xxxxx"
      }
    }
  }
}

# 通过命令行指定 MCP 配置
claude --mcp-config ./custom-mcp.json

// .claude/mcp_settings.json
{
  "mcpServers": {
    "postgres": {
      "command": "npx",
      "args": ["-y", "@anthropic/mcp-postgres", "postgresql://localhost/mydb"]
    }
  }
}

> 查询最近7天注册的用户数量，按天分组

Claude Code: [使用 PostgreSQL MCP]
  → Executing: SELECT DATE(created_at), COUNT(*) FROM users
    WHERE created_at > NOW() - INTERVAL '7 days'
    GROUP BY DATE(created_at) ORDER BY 1

  结果：
  | 日期       | 注册数 |
  |:-----------|:-------|
  | 2026-08-22 | 45     |
  | 2026-08-23 | 52     |
  | 2026-08-24 | 38     |
  | 2026-08-25 | 61     |
  | 2026-08-26 | 49     |
  | 2026-08-27 | 55     |
  | 2026-08-28 | 42     |

// custom-mcp-server.ts
import { Server } from "@anthropic/mcp";

const server = new Server({
  name: "weather",
  version: "1.0.0",
});

server.tool("get_weather", "Get current weather for a city", {
  city: { type: "string", description: "City name" },
}, async ({ city }) => {
  const response = await fetch(
    `https://api.weather.com/current?city=${city}`
  );
  const data = await response.json();
  return {
    content: [{
      type: "text",
      text: `${city}: ${data.temperature}°C, ${data.condition}`
    }]
  };
});

server.start();

// .claude/mcp_settings.json
{
  "mcpServers": {
    "weather": {
      "command": "npx",
      "args": ["tsx", "./custom-mcp-server.ts"]
    }
  }
}

// Alice 的项目 MCP 配置
{
  "mcpServers": {
    "postgres-read": {
      "command": "npx",
      "args": ["-y", "@anthropic/mcp-postgres"],
      "env": {
        "DATABASE_URL": "postgresql://readonly:pass@localhost/dev"
      }
    },
    "github": {
      "command": "npx",
      "args": ["-y", "@anthropic/mcp-github"],
      "env": {
        "GITHUB_TOKEN": "${GITHUB_TOKEN}"
      }
    },
    "browser": {
      "command": "npx",
      "args": ["-y", "@anthropic/mcp-browser"]
    }
  }
}

# Alice 使用 MCP 完成完整工作流

> 查询数据库中活跃用户数，
> 在 GitHub 创建一个对应的 issue，
> 然后打开浏览器验证修复后的页面

Claude Code:
  → [PostgreSQL MCP] 查询活跃用户数：12,450
  → [GitHub MCP] 创建 issue #342: 活跃用户统计优化
  → [Browser MCP] 打开 https://localhost:3000/dashboard
  → 页面截图验证：数据正确显示 ✓