> ## Documentation Index
> Fetch the complete documentation index at: https://mintlify-poc.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# locf()

> Fill in missing values by carrying the last observed value forward

<Icon icon="tag" iconType="duotone" /> Since [1.1.1][tsdb-1.1.1]

Fill in missing values by carrying the last observed value forward.
Use in the same query as [`time_bucket_gapfill`][time_bucket_gapfill].
`locf` cannot be nested inside another function call.

## Arguments

The syntax is:

```sql theme={"dark"}
SELECT locf(
    value = <anyelement>,
    prev = <anyelement>,
    treat_null_as_missing = true | false
);
```

| Name                    | Type        | Default | Required | Description                                                                                                                                                                                                                                                                                                                                                  |
| ----------------------- | ----------- | ------- | -------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |
| `value`                 | ANY ELEMENT | -       | ✔        | The value to carry forward                                                                                                                                                                                                                                                                                                                                   |
| `prev`                  | EXPRESSION  | -       | -        | If no previous value is available for gapfilling, use the `prev` lookup expression to get a previous value. For example, you can use `prev` to fill in the first bucket in a queried time range. The expression must return just a value (not a tuple as expected by the [`interpolate`][interpolate] function) with the same type as the `value` parameter. |
| `treat_null_as_missing` | BOOLEAN     | -       | -        | When `true`, `NULL` values are ignored, and only non-`NULL` values are carried forward.                                                                                                                                                                                                                                                                      |

## Returns

| Column | Type        | Description                                                          |
| ------ | ----------- | -------------------------------------------------------------------- |
| `locf` | ANY ELEMENT | The gapfilled value. The return type matches the input `value` type. |

[interpolate]: /api-reference/timescaledb/hyperfunctions/time_bucket_gapfill/interpolate

[time_bucket_gapfill]: /api-reference/timescaledb/hyperfunctions/time_bucket_gapfill/time_bucket_gapfill

[tsdb-1.1.1]: https://github.com/timescale/timescaledb/releases/tag/1.1.1