快速数据库结构生成助手

以下是根据您的输入生成的数据库结构设计：

```json
{
  "databaseSchema": "CREATE TABLE users (\n    id INT PRIMARY KEY,\n    username VARCHAR(255) NOT NULL,\n    email VARCHAR(255) NOT NULL,\n    created_at DATETIME NOT NULL\n);\n\nCREATE TABLE orders (\n    id INT PRIMARY KEY,\n    order_date DATETIME NOT NULL,\n    total_amount DECIMAL(10,2) NOT NULL,\n    user_id INT NOT NULL,\n    FOREIGN KEY (user_id) REFERENCES users(id)\n);",
  "tables": [
    {
      "tableName": "users",
      "fields": [
        {"name": "id", "type": "INT", "isPrimaryKey": true},
        {"name": "username", "type": "VARCHAR(255)", "isPrimaryKey": false},
        {"name": "email", "type": "VARCHAR(255)", "isPrimaryKey": false},
        {"name": "created_at", "type": "DATETIME", "isPrimaryKey": false}
      ]
    },
    {
      "tableName": "orders",
      "fields": [
        {"name": "id", "type": "INT", "isPrimaryKey": true},
        {"name": "order_date", "type": "DATETIME", "isPrimaryKey": false},
        {"name": "total_amount", "type": "DECIMAL(10,2)", "isPrimaryKey": false},
        {"name": "user_id", "type": "INT", "isPrimaryKey": false}
      ]
    }
  ],
  "relationships": [
    "orders.user_id -> users.id"
  ]
}
```

### 详细说明：
- 表 `users` 的字段：
  - **id**：主键，类型为 `INT`。
  - **username**：用户名称，类型为 `VARCHAR(255)`。
  - **email**：用户邮箱，类型为 `VARCHAR(255)`。
  - **created_at**：用户创建时间，类型为 `DATETIME`。

- 表 `orders` 的字段：
  - **id**：主键，类型为 `INT`。
  - **order_date**：订单日期，类型为 `DATETIME`。
  - **total_amount**：订单总金额，类型为 `DECIMAL(10,2)`。
  - **user_id**：外键字段，用于关联 `users` 表的 `id`。

- 表间关系：
  - `orders.user_id` 是 `users.id` 的外键，用于表示订单属于哪个用户。

### DDL语句：
生成的 DDL 语句可以直接在大多数主流数据库（如 MySQL、PostgreSQL）中执行，以创建相关的表结构。

```json
{
  "databaseSchema": "CREATE TABLE products (\n    product_id INT NOT NULL PRIMARY KEY,\n    product_name VARCHAR(255) NOT NULL,\n    price DECIMAL(10, 2) NOT NULL,\n    stock INT NOT NULL\n);",
  "tables": [
    {
      "tableName": "products",
      "fields": [
        {"name": "product_id", "type": "INT", "isPrimaryKey": true},
        {"name": "product_name", "type": "VARCHAR(255)", "isPrimaryKey": false},
        {"name": "price", "type": "DECIMAL(10, 2)", "isPrimaryKey": false},
        {"name": "stock", "type": "INT", "isPrimaryKey": false}
      ]
    }
  ],
  "relationships": []
}
```

```json
{
  "databaseSchema": "CREATE TABLE orders (\n  order_id INT PRIMARY KEY,\n  user_id INT NOT NULL,\n  total_price DECIMAL(10, 2) NOT NULL,\n  order_date DATETIME NOT NULL,\n  FOREIGN KEY (user_id) REFERENCES users(id)\n);",
  "tables": [
    {
      "tableName": "orders",
      "fields": [
        {"name": "order_id", "type": "INT", "isPrimaryKey": true},
        {"name": "user_id", "type": "INT", "isPrimaryKey": false},
        {"name": "total_price", "type": "DECIMAL(10, 2)", "isPrimaryKey": false},
        {"name": "order_date", "type": "DATETIME", "isPrimaryKey": false}
      ]
    }
  ],
  "relationships": [
    "orders.user_id -> users.id"
  ]
}
```