# $sum

`$sum` computes the total of a field across matching documents.

If `missing` is set, missing fields contribute that fallback value.

By default, `$sum` returns `0` when no values are collected — either no documents match, or the matching documents all have a missing/null value for the field and no `missing` fallback is set. Set `nullIfNoMatch` to `true` to return `null` instead, so you can distinguish that case from a real total of zero.

### Compatibility

| Field Type | Supported |
|------------|-----------|
| TEXT | No |
| U64/I64/F64 | Yes |
| DATE | Yes |
| BOOL | Yes |
| KEYWORD | No |
| FACET | No |

Field must be `FAST`.

### Arguments

| Argument | Type | Required | Description |
|----------|------|----------|-------------|
| `field` | `string` | Yes | Field to aggregate. |
| `missing` | `number` | No | Fallback value for missing fields. |
| `nullIfNoMatch` | `boolean` | No | Return `null` instead of `0` when no values are collected. Default: `false`. |

<Tabs>

<Tab title="TypeScript">
```ts
await index.aggregate({
  aggregations: {
    total_price: { $sum: { field: "price", nullIfNoMatch: true } },
  },
});
```
</Tab>

<Tab title="Python">
```python
index.aggregate(
    aggregations={
        "total_price": {
            "$sum": {"field": "price", "nullIfNoMatch": True}
        }
    },
)
```
</Tab>

<Tab title="Redis CLI">
```bash
SEARCH.AGGREGATE products '{}' '{"total_price": {"$sum": {"field": "price", "nullIfNoMatch": true}}}'
```
</Tab>

</Tabs>

### Output

```json
{ "total_price": { "value": 360 } }
```

With `nullIfNoMatch: true`, an aggregation with no collected values (for example, the filter above matches no documents) returns:

```json
{ "total_price": { "value": null } }
```

Without `nullIfNoMatch`, the same aggregation returns `0`. This option does not change results where at least one value was collected, including a real sum of zero.