---
title: "REFRESH COLUMN"
sidebarTitle: "REFRESH COLUMN"
description: "Filling a computed column: idempotent, scoped, and resumable."
icon: arrows-rotate
keywords: ["refresh column", "backfill", "computed column"]
availability:
  embedded: unavailable
  enterprise: available
---

A LanceDB extension with no DataFusion equivalent. It is what makes
[feature engineering](/feature-engineering) reachable from SQL: a column
declared by [DDL](/sql/ddl/table#computed-column) starts empty, and a refresh fills it.

```sql
REFRESH COLUMN <column> ON [TABLE] <table>
  [WHERE <predicate>]
  [WITH (<option> = <value> [, ...])]
```

```sql
REFRESH COLUMN doubled ON my_table
REFRESH COLUMN embedding ON documents WHERE created_at > '2026-01-01'
```

A refresh gives values to rows that lack them, recomputes rows whose inputs
changed, and **leaves other filled rows alone**. That makes it idempotent, cheap
to repeat as data arrives, and safe to re-run after a failure, though a re-run
can recompute values the failed run had already written.

`WHERE` scopes the refresh, which is how you fill a slice and check it before
committing to the whole table.

## Options {#options}

| Option | Meaning |
| --- | --- |
| `num_workers` | how many workers to use |
| `cpu_millis` | CPU budget per worker |
| `memory_bytes` | memory budget per worker |
| `gpu_count` | GPUs per worker |
| `batch_size` | rows a worker takes at a time |
| `error_policy` | `'skip'` continues past failing rows instead of failing the job |

```sql
REFRESH COLUMN embedding ON documents
  WITH (cpu_millis = 8000, memory_bytes = 17179869184, gpu_count = 2)
```

`num_workers` sets a count; the budget options size each worker. They are
alternatives rather than a pair.

{/*
Draft for the Functions release.

<Note>
`error_policy` and `num_workers` are refused for a column filled by a registered
[function](/management/function) with its own resource budget -- use the CPU,
memory and GPU options there.
</Note>
*/}

## Watching a refresh {#watching}

A refresh submits work that outlives the call. Track it with
[`SHOW JOBS`](/sql/ddl/job#show), and diagnose failures with
[`SHOW ERRORS`](/sql/ddl/job#errors).

## See also {#see-also}

<CardGroup cols={2}>
  <Card title="Refresh a computed column" icon="arrows-rotate" href="/feature-engineering/refresh-column">
    The same operation from the SDKs, and what a refresh guarantees.
  </Card>
  <Card title="Table" icon="table" href="/sql/ddl/table#alter">
    Declaring the columns this fills.
  </Card>
  <Card title="REFRESH MATERIALIZED VIEW" icon="arrows-rotate" href="/sql/dml/refresh-materialized-view">
    Bringing a view's stored result up to date, instead of a column.
  </Card>
</CardGroup>