# Database Schema Change Request: Exam Structure Support

## 1. Table: `exams`

### Change
**Add Column**: `structure`

### Details
- **Type**: `JSON`
- **Nullable**: `TRUE` (Default: `NULL`)

### Reason
To support hierarchical exam structures (e.g., Sections/Groups containing Questions). The existing flat `exam_questions` table only supports a simple list of questions and is insufficient for complex exam layouts (e.g., "Part A: Reading", "Part B: Writing").

### Before vs After

**Before**:
`exams` table only stores metadata (`title`, `description`, etc.). Question ordering relies solely on `exam_questions.order`.

**After**:
`exams` table includes `structure` column to store the full tree representation:
```json
[
  { "id": "uuid-1", "type": "group", "title": "Section A", "children": [...] },
  { "id": "uuid-2", "type": "question", "questionId": "q1", "score": 10 }
]
```
*Note: `exam_questions` table is retained for relational integrity and efficient querying of question usage, but the presentation order/structure is now driven by this new JSON column.*

---

## 2. Table: `questions_to_knowledge_points`

### Change
**Rename Foreign Key Constraints**

### Details
- Rename constraint for `question_id` to `q_kp_qid_fk`
- Rename constraint for `knowledge_point_id` to `q_kp_kpid_fk`

### Reason
The default generated foreign key names (e.g., `questions_to_knowledge_points_knowledge_point_id_knowledge_points_id_fk`) exceed the MySQL identifier length limit (64 characters), causing migration failures.

### Before vs After

**Before**:
- FK Name: `questions_to_knowledge_points_question_id_questions_id_fk` (Too long)
- FK Name: `questions_to_knowledge_points_knowledge_point_id_knowledge_points_id_fk` (Too long)

**After**:
- FK Name: `q_kp_qid_fk`
- FK Name: `q_kp_kpid_fk`