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Jack Ye
ddb318567a
## Summary - Complete the SQL reference: `ATTACH DATABASE`, the `CHANGES` clause, and `dedupe()`/`duplicate_pairs()` (verified against current sophon source; these were recently renamed from `vector_dedup`/`vector_duplicate_pairs`). Fix the blob-column default-projection claim and add the previously undocumented `blob_descriptor()`. - Enrich the gated Functions draft (still `.mintignore`'d, pre-release): chained Functions over blob outputs, GPU-produced blobs, Secrets, multi-input/output binding, `code=[module]` packaging. - Upgrade the materialized-view and computed-column auto-refresh drafts with precise, verified catch-up semantics, and add the missing `ALTER MATERIALIZED VIEW` / `CREATE ... WITH(...)` sections (also gated — the automatic-refresh scheduler is still dev/staging-only). - Thread one running example (video frames → GPU extract/caption → dedup → auto-refreshing materialized view) through Functions, materialized views, and the LeRobotDataset integration guide instead of a separate tutorial. - Rename "LanceDB OSS"/"OSS" to "LanceDB Embedded"/"Embedded" throughout (52 files); activate the existing availability-comparison mechanism on `basics/offerings.mdx` for a full feature-by-feature comparison table.
83 lines
2.7 KiB
Plaintext
83 lines
2.7 KiB
Plaintext
---
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title: "REFRESH COLUMN"
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sidebarTitle: "REFRESH COLUMN"
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description: "Filling a computed column: idempotent, scoped, and resumable."
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icon: arrows-rotate
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keywords: ["refresh column", "backfill", "computed column"]
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availability:
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embedded: unavailable
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enterprise: available
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---
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A LanceDB extension with no DataFusion equivalent. It is what makes
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[feature engineering](/feature-engineering) reachable from SQL: a column
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declared by [DDL](/sql/ddl/table#computed-column) starts empty, and a refresh fills it.
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```sql
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REFRESH COLUMN <column> ON [TABLE] <table>
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[WHERE <predicate>]
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[WITH (<option> = <value> [, ...])]
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```
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```sql
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REFRESH COLUMN doubled ON my_table
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REFRESH COLUMN embedding ON documents WHERE created_at > '2026-01-01'
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```
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A refresh gives values to rows that lack them, recomputes rows whose inputs
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changed, and **leaves other filled rows alone**. That makes it idempotent, cheap
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to repeat as data arrives, and safe to re-run after a failure, though a re-run
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can recompute values the failed run had already written.
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`WHERE` scopes the refresh, which is how you fill a slice and check it before
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committing to the whole table.
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## Options {#options}
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| Option | Meaning |
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| --- | --- |
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| `num_workers` | how many workers to use |
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| `cpu_millis` | CPU budget per worker |
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| `memory_bytes` | memory budget per worker |
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| `gpu_count` | GPUs per worker |
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| `batch_size` | rows a worker takes at a time |
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| `error_policy` | `'skip'` continues past failing rows instead of failing the job |
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```sql
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REFRESH COLUMN embedding ON documents
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WITH (cpu_millis = 8000, memory_bytes = 17179869184, gpu_count = 2)
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```
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`num_workers` sets a count; the budget options size each worker. They are
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alternatives rather than a pair.
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{/*
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Draft for the Functions release.
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<Note>
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`error_policy` and `num_workers` are refused for a column filled by a registered
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[function](/management/function) with its own resource budget -- use the CPU,
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memory and GPU options there.
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</Note>
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*/}
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## Watching a refresh {#watching}
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A refresh submits work that outlives the call. Track it with
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[`SHOW JOBS`](/sql/ddl/job#show), and diagnose failures with
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[`SHOW ERRORS`](/sql/ddl/job#errors).
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## See also {#see-also}
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<CardGroup cols={2}>
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<Card title="Refresh a computed column" icon="arrows-rotate" href="/feature-engineering/refresh-column">
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The same operation from the SDKs, and what a refresh guarantees.
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</Card>
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<Card title="Table" icon="table" href="/sql/ddl/table#alter">
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Declaring the columns this fills.
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</Card>
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<Card title="REFRESH MATERIALIZED VIEW" icon="arrows-rotate" href="/sql/dml/refresh-materialized-view">
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Bringing a view's stored result up to date, instead of a column.
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</Card>
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</CardGroup>
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