erDiagram USER ||--o{ JOURNAL : owns USER { string user_id PK "用户ID" string username "用户名" string email "邮箱" datetime created_at "创建时间" } JOURNAL ||--o{ ENTRY : contains JOURNAL { string journal_id PK "日记本ID" string user_id FK "所属用户" string title "日记本名称" datetime created_at "创建时间" } ENTRY }o--o{ TAG : has ENTRY { string entry_id PK "日记ID" string journal_id FK "所属日记本" string title "日记标题" text content "日记内容" datetime created_at "创建时间" datetime updated_at "更新时间" } TAG { string tag_id PK "标签ID" string name "标签名称" }