# MongoServerError: 无法创建索引 'idx_email_unique'：字段 'email' 上已存在一个具有不同选项的唯一索引

- **ID:** `database/mongodb-cannot-create-index-duplicate-key`
- **领域:** database
- **类别:** config_error
- **验证级别:** ai_generated
- **修复率:** 90%

## 根因

同一字段上已存在的唯一索引与新创建的索引具有不同的选项（例如，排序规则、稀疏、部分过滤器表达式），导致冲突。

## 版本兼容性

| 版本 | 状态 | 引入 | 弃用 |
|------|------|------|------|
| MongoDB 5.0 | active | — | — |
| MongoDB 6.0 | active | — | — |
| MongoDB 7.0 | active | — | — |
| MongoDB 8.0 | active | — | — |

## 解决方案

1. ```
   列出集合上的现有索引：`db.collection.getIndexes()`。识别冲突索引并删除它：`db.collection.dropIndex('idx_email_unique')`。然后使用所需选项创建新索引：`db.collection.createIndex({email: 1}, {unique: true, name: 'idx_email_unique', collation: {locale: 'en', strength: 2}})`
   ```
2. ```
   如果现有索引具有不同选项但您想保留它，将新索引重命名为不同名称：`db.collection.createIndex({email: 1}, {unique: true, name: 'idx_email_unique_v2'})`
   ```

## 无效尝试

- **Drop the existing index with db.collection.dropIndex() and recreate it with the same name but different options** — If the existing index is being used by an application, dropping it may cause query performance degradation or application errors until the new index is created (50% 失败率)
- **Create the index with the force: true option** — MongoDB does not support a 'force' option for index creation; this will result in a syntax error (100% 失败率)
- **Ignore the error and assume the index already exists** — The existing index may have different collation or options, leading to unexpected behavior in queries or uniqueness enforcement (60% 失败率)