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Jack Ye
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OSS docs now own the full usage content for features that only run against an Enterprise deployment, since the client interface itself lives here; Enterprise docs keep only the parts specific to its own behavior. Sophon's overlay for these five pages is dropped since the OSS versions are now the complete reference. SQL Reference is restructured to match an object-type SQL manual (DDL by object, then DML, then DQL, then Expressions) instead of the old flat, loosely-ordered page list, absorbing the SQL client-connection guide and FTS-via-SQL examples into it.
99 lines
3.1 KiB
Plaintext
99 lines
3.1 KiB
Plaintext
---
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title: "View"
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sidebarTitle: "View"
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description: "CREATE VIEW and DROP VIEW — a saved query, evaluated when read."
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icon: eye
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keywords: ["create view", "drop view", "sql", "catalog"]
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---
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<Badge color="red">Enterprise</Badge> [SQL runs on a deployment.](/sql)
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A view stores a **query**, not rows. Reading it runs the query against current
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data, so a view is never stale -- and never faster than the query it wraps. It
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is the counterpart to a [materialized view](/sql/ddl/materialized-view), which
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stores rows and is brought up to date by a refresh; both are
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[catalog objects](/basics/catalog) defined by a query, differing only in when
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that query runs.
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There is no SDK method for a view, because the thing it stores *is* a SQL
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statement.
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## CREATE VIEW {#create}
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```sql
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CREATE VIEW "recent_matches" AS
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SELECT t1.floats
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FROM "documents" AS t1
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INNER JOIN "categories" AS t2 ON t1.ints = t2.ints
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```
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The statement returns the view's schema -- column name, data type, nullability
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-- resolved from the query at creation time. Anything the
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[dialect](/sql/functions) supports can define one: joins, predicates,
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aggregates, window functions.
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## Reading one {#reading}
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A view is queried like a table:
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```sql
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SELECT * FROM "recent_matches" WHERE floats > 0.5
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```
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Predicates applied to the view compose with the query inside it rather than
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filtering its output afterwards, so a selective filter does not pay for rows
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the view would have produced and then discarded.
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## DROP VIEW {#drop}
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```sql
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DROP VIEW "recent_matches"
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```
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Removes the saved query. Unlike dropping a table, no data is removed -- there
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was none to begin with.
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## Listing {#listing}
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Views and tables share a namespace, and both are things you can query. The
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catalog distinguishes them:
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| --- | --- |
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| view names | the views in the database |
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| table names | the tables |
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| relation names | everything queryable -- both |
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Use the relation listing when the question is "what can I select from," and the
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separate listings when the distinction matters -- before dropping, for
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instance, since dropping a view removes only the saved query while dropping a
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table removes data.
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## Choosing between a view and a materialized view {#choosing}
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| | View | Materialized view |
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| --- | --- | --- |
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| Stores | the query | the rows |
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| Freshness | always current | as of the last refresh |
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| Read cost | the full query, every read | a 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 stale rows would
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be wrong. Reach for a **materialized view** when the query is expensive and the
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data changes less often than it is read.
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The privileges are separate too: `CREATE_VIEW` and `CREATE_MATERIALIZED_VIEW`
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are distinct grants on a namespace, so the ability to create one does not imply
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the other. See [Authorization](/governance/authorization).
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## What to read next {#next}
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<CardGroup cols={2}>
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<Card title="Materialized View" icon="table" href="/sql/ddl/materialized-view">
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The stored-rows counterpart.
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</Card>
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<Card title="Management" icon="folder-tree" href="/management">
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Where views fit among the other catalog objects.
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</Card>
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</CardGroup>
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