# sqlalchemy.exc.IntegrityError：(psycopg2.errors.UniqueViolation) 重复键值违反唯一约束 "users_email_key"

- **ID:** `python/sqlalchemy-integrity-error-duplicate`
- **领域:** python
- **类别:** data_error
- **验证级别:** ai_generated
- **修复率:** 80%

## 根因

在唯一列中插入重复值。

## 版本兼容性

| 版本 | 状态 | 引入 | 弃用 |
|------|------|------|------|
| 3.x | active | — | — |

## 解决方案

1. **Check for existing record before insert.** (95% 成功率)
   ```
   existing = session.query(User).filter_by(email='test@example.com').first()
if not existing:
    session.add(User(email='test@example.com'))
session.commit()
   ```
2. **Use ON CONFLICT DO NOTHING via SQLAlchemy dialect.** (90% 成功率)
   ```
   from sqlalchemy.dialects.postgresql import insert
stmt = insert(User).values(email='test@example.com').on_conflict_do_nothing()
session.execute(stmt)
session.commit()
   ```

## 无效尝试

- **Catching exception and ignoring without rollback.** — Transaction remains in aborted state; subsequent queries fail. (90% 失败率)
- **Using session.merge() without checking for conflicts.** — Merge may still raise IntegrityError if primary key conflicts. (60% 失败率)