docs: erd

Author: pmh5574

docs/week2/004-erd.md

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+```mermaid
+erDiagram
+    users {
+        bigint id PK
+        varchar user_id UK
+        varchar email UK
+        varchar gender
+        date birthday
+        timestamp created_at
+        timestamp updated_at
+        timestamp deleted_at
+    }
+    products {
+        bigint id PK
+        varchar name
+        bigint price
+        bigint brand_id FK
+        timestamp created_at
+        timestamp updated_at
+        timestamp deleted_at
+    }
+    stocks {
+        bigint id PK
+        int quantity
+        bigint product_id FK
+        timestamp created_at
+        timestamp updated_at
+    }
+    stock_histories {
+        bigint id PK
+        int before_quantity
+        int quantity
+        int after_quantity
+        varchar stock_type
+        bigint stock_id FK
+        timestamp created_at
+        timestamp updated_at
+    }
+    brands {
+        bigint id PK
+        varchar name
+        timestamp created_at
+        timestamp updated_at
+        timestamp deleted_at
+    }
+    likes {
+        bigint user_id PK, FK
+        bigint product_id PK, FK
+        timestamp created_at
+        timestamp updated_at
+    }
+    points {
+        bigint id PK
+        bigint point
+        bigint user_id FK
+        timestamp created_at
+        timestamp updated_at
+        timestamp deleted_at
+    }
+    point_histories {
+        bigint id PK
+        bigint before_point
+        bigint amount
+        bigint after_point
+        varchar point_type
+        bigint point_id FK
+        timestamp created_at
+        timestamp updated_at
+    }
+    orders {
+        bigint id PK
+        bigint total_price
+        varchar order_status
+        bigint user_id FK
+        timestamp created_at
+        timestamp updated_at
+    }
+    order_items {
+        bigint id PK
+        int quantity
+        varchar product_name
+        bigint product_price
+        bigint order_id FK
+        bigint product_id FK
+        timestamp created_at
+        timestamp updated_at
+    }
+
+    users ||--o{ likes: ""
+    users ||--o{ points: ""
+    users ||--o{ orders: ""
+    brands ||--o{ products: ""
+    products ||--|| stocks: ""
+    stocks ||--o{ stock_histories: ""
+    points ||--o{ point_histories: ""
+    orders ||--o{ order_items: ""
+    products ||--o{ likes: ""
+```