# sqlalchemy.exc.MultipleResultsFound: Multiple rows were found when exactly one was required

- **ID:** `python/flask-sqlalchemy-multiple-results-found`
- **Domain:** python
- **Category:** data_error
- **Verification:** ai_generated
- **Fix Rate:** 80%

## Root Cause

query.one() or scalar_one() used on a query that returns multiple rows, often due to missing unique constraint or duplicate data.

## Version Compatibility

| Version | Status | Introduced | Deprecated |
|---------|--------|------------|------------|
| 3.x | active | — | — |

## Workarounds

1. **** (88% success)
   ```
   Use .one_or_none() and handle None explicitly
   ```
2. **** (92% success)
   ```
   Add unique constraint: email = db.Column(db.String, unique=True)
   ```

## Dead Ends

- **** — Silently returns arbitrary row; hides data bug. (50% fail)
- **** — Same silent-truncation risk. (55% fail)