# Moose / Olap / Ttl Documentation – Python

## Included Files
1. moose/olap/ttl/ttl.mdx

## ttl

Source: moose/olap/ttl/ttl.mdx

## TTL (Time-to-Live) for ClickHouse Tables

Moose lets you declare ClickHouse TTL directly in your data model:
- Table-level TTL via the `ttl` option on `OlapTable` config
- Column-level TTL via `ClickHouseTTL` on individual fields

### When to use TTL
- Automatically expire old rows to control storage cost
- Mask or drop sensitive columns earlier than the full row expiry

### TypeScript

```ts

interface Event {
  id: Key<string>;
  timestamp: DateTime;
  email: string & ClickHouseTTL<"timestamp + INTERVAL 30 DAY">; // column TTL
}

);
```

### Python

```python
from typing import Annotated
from moose_lib import OlapTable, OlapConfig, Key, ClickHouseTTL
from pydantic import BaseModel
from datetime import datetime

class Event(BaseModel):
    id: Key[str]
    timestamp: datetime
    email: Annotated[str, ClickHouseTTL("timestamp + INTERVAL 30 DAY")]

events = OlapTable[Event](
    "Events",
    OlapConfig(
        order_by_fields=["id", "timestamp"],
        ttl="timestamp + INTERVAL 90 DAY DELETE",
    ),
)
```

### Notes
- Expressions must be valid ClickHouse TTL expressions, but do not include the leading `TTL` keyword.
- Column TTLs are independent from the table TTL and can be used together.
- Moose will apply TTL changes via migrations using `ALTER TABLE ... MODIFY TTL` and `MODIFY COLUMN ... TTL`.

### Related
- See `Modeling Tables` for defining your schema
- See `Applying Migrations` to roll out TTL changes