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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.
74 lines
2.8 KiB
Plaintext
74 lines
2.8 KiB
Plaintext
---
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title: "Create a view"
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sidebarTitle: "Create View"
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description: "Define a derived dataset as a saved query, with no storage or refresh of its own."
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icon: eye
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keywords: ["view", "create view", "feature engineering", "saved query"]
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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 view is the lightest way to derive a feature-engineered dataset: it stores
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a **query**, not rows, so there is nothing to refresh and nothing that can
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fall out of date. Reach for one before
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[a computed column](/feature-engineering/add-computed-column) or
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[a materialized view](/feature-engineering/materialized-views) when the
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underlying query is cheap enough to simply re-run on every read.
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## Define a view {#create}
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A view over a products table, selecting and deriving a few columns:
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```sql
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CREATE VIEW "discounted_products" AS
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SELECT id, name, price, price * 0.9 AS sale_price
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FROM "products"
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WHERE in_stock = true
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```
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The statement resolves the view's schema from the query at creation time.
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Anything the [SQL dialect](/sql/functions) supports can define one: joins,
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predicates, aggregates, window functions -- the same expressiveness as
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[a computed column's](/feature-engineering/add-computed-column#expressions)
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SQL expression, just over a whole derived table instead of one column.
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## Read it like a table {#reading}
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```sql
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SELECT * FROM "discounted_products" WHERE sale_price < 20
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```
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Every read runs the saved query against current data, so `sale_price`
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reflects whatever `price` is right now -- there is no staleness window to
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reason about, unlike a materialized view between refreshes. A predicate
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applied when reading the view composes with the query inside it, rather than
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filtering the view's output afterward, so a selective filter does not pay
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for rows the view would have produced and then discarded.
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## When to use a view instead {#choosing}
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| | View | Computed column / materialized view |
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| --- | --- | --- |
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| Stores | the query | derived values |
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| Freshness | always current | as of the last refresh |
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| Read cost | the full query, every read | a column or table scan |
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| Write cost | none | a refresh |
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Reach for a view when the query is cheap, or when reading a stale value would
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be wrong for the workload. Reach for a computed column or a materialized view
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when the query is expensive and the data changes less often than it is read.
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See [View](/sql/ddl/view#choosing) for the full SQL reference comparison,
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including the separate privileges each one needs.
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## What to read next {#next}
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<CardGroup cols={2}>
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<Card title="View" icon="eye" href="/sql/ddl/view">
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CREATE VIEW, DROP VIEW, and listing views alongside tables.
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</Card>
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<Card title="Create a materialized view" icon="table" href="/feature-engineering/materialized-views">
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The stored-rows counterpart, and when a refresh is worth paying for.
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</Card>
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</CardGroup>
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