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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.
77 lines
2.7 KiB
Plaintext
77 lines
2.7 KiB
Plaintext
---
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title: "Changes since a version"
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sidebarTitle: "Changes"
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description: "CHANGES: read the rows appended to a table since an earlier version."
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icon: clock-rotate-left
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keywords: ["changes", "append", "incremental", "cdc", "version"]
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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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`CHANGES` reads the rows appended to a table since an earlier
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[version](/management/table#versioning), without rescanning rows that were
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already there:
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```sql
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SELECT * FROM events CHANGES (INFORMATION => APPEND_ONLY) AT (VERSION => 42)
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```
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This returns the rows appended after version 42, up to the table's current
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version at the time the query runs.
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## Strictly append-only {#strict}
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The clause is named for what it requires, not just what it does: every
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change to the table between the starting version and the current one must
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be an append. If any of them inserted with changes other than a pure append
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-- an update, a delete, a merge -- the query is refused rather than silently
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returning an incomplete or wrong result. Re-run it with a later starting
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version that is itself after the non-append write, or read the table in full
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instead of incrementally.
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`INFORMATION => APPEND_ONLY` is the only supported value: it names what kind
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of history the clause is willing to read, not a choice among several. `AT
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(VERSION => ...)` takes a positive integer; there is no `AT (TIMESTAMP =>
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...)` form for this clause, unlike other version qualifiers.
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## Where the clause can go {#placement}
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It attaches to a table in `FROM`, including inside a subquery, a CTE, a join,
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a set operation, or `EXPLAIN`:
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```sql
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WITH recent AS (
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SELECT * FROM events CHANGES (INFORMATION => APPEND_ONLY) AT (VERSION => 42)
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)
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SELECT count(*) FROM recent
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SELECT * FROM events CHANGES (INFORMATION => APPEND_ONLY) AT (VERSION => 10) a
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JOIN events CHANGES (INFORMATION => APPEND_ONLY) AT (VERSION => 20) b
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ON a.id = b.id
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```
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Each occurrence of a table keeps its own starting version, even when the same
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table is referenced more than once in one statement.
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## Unsupported forms {#refused}
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| --- | --- |
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| `CHANGES (INFORMATION => DEFAULT)` | only `APPEND_ONLY` is supported |
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| `AT (TIMESTAMP => ...)` | only `AT (VERSION => ...)` is supported |
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| `AT (VERSION => 0)` | the starting version must be positive |
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| `... END (VERSION => ...)` | not supported; the current version is always the end |
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| `CHANGES ... TABLESAMPLE (...)` | cannot be combined on the same table reference |
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## What to read next {#next}
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<CardGroup cols={2}>
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<Card title="Table" icon="table" href="/sql/ddl/table">
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CREATE, ALTER, CLONE and versioning basics.
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</Card>
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<Card title="Select" icon="magnifying-glass" href="/sql/dql/select">
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The rest of the query grammar this clause attaches to.
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</Card>
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</CardGroup>
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