d59980783e
### What changes were proposed in this pull request? Added document for CREATE VIEW command. ### Why are the changes needed? As a reference to syntax and examples of CREATE VIEW command. ### How was this patch tested? Documentation update. Verified manually. Closes #25543 from amanomer/spark-28795. Lead-authored-by: aman_omer <amanomer1996@gmail.com> Co-authored-by: Xiao Li <gatorsmile@gmail.com> Co-authored-by: Aman Omer <amanomer1996@gmail.com> Signed-off-by: Xiao Li <gatorsmile@gmail.com>
83 lines
3.2 KiB
Markdown
83 lines
3.2 KiB
Markdown
---
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layout: global
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title: CREATE VIEW
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displayTitle: CREATE VIEW
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license: |
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Licensed to the Apache Software Foundation (ASF) under one or more
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contributor license agreements. See the NOTICE file distributed with
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this work for additional information regarding copyright ownership.
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The ASF licenses this file to You under the Apache License, Version 2.0
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(the "License"); you may not use this file except in compliance with
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the License. You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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---
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### Description
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Views are based on the result-set of an `SQL` query. `CREATE VIEW` constructs
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a virtual table that has no physical data therefore other operations like
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`ALTER VIEW` and `DROP VIEW` only change metadata.
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### Syntax
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{% highlight sql %}
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CREATE [OR REPLACE] [[GLOBAL] TEMPORARY] VIEW [IF NOT EXISTS] [db_name.]view_name
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create_view_clauses
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AS query;
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{% endhighlight %}
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### Parameters
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<dl>
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<dt><code><em>OR REPLACE</em></code></dt>
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<dd>If a view of same name already exists, it will be replaced.</dd>
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</dl>
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<dl>
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<dt><code><em>[GLOBAL] TEMPORARY</em></code></dt>
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<dd>TEMPORARY views are session-scoped and will be dropped when session ends
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because it skips persisting the definition in the underlying metastore, if any.
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GLOBAL TEMPORARY views are tied to a system preserved temporary database `global_temp`.</dd>
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</dl>
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<dl>
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<dt><code><em>IF NOT EXISTS</em></code></dt>
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<dd>Creates a view if it does not exists.</dd>
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</dl>
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<dl>
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<dt><code><em>create_view_clauses</em></code></dt>
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<dd>These clauses are optional and order insensitive. It can be of following formats.
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<ul>
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<li><code>[(column_name [COMMENT column_comment], ...) ]</code> to specify column-level comments.</li>
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<li><code>[COMMENT view_comment]</code> to specify view-level comments.</li>
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<li><code>[TBLPROPERTIES (property_name = property_value, ...)]</code> to add metadata key-value pairs.</li>
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</ul>
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</dd>
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</dl>
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<dl>
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<dt><code><em>query</em></code></dt>
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<dd>A <a href="sql-ref-syntax-qry-select.md">SELECT</a> statement that constructs the view from base tables or other views.</dd>
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</dl>
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### Examples
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{% highlight sql %}
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-- Create or replace view for `experienced_employee` with comments.
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CREATE OR REPLACE VIEW experienced_employee
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(ID COMMENT 'Unique identification number', Name)
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COMMENT 'View for experienced employees'
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AS SELECT id, name FROM all_employee
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WHERE working_years > 5;
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-- Create a global temporary view `subscribed_movies` if it does not exist.
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CREATE GLOBAL TEMPORARY VIEW IF NOT EXISTS subscribed_movies
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AS SELECT mo.member_id, mb.full_name, mo.movie_title
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FROM movies AS mo INNER JOIN members AS mb
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ON mo.member_id = mb.id;
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{% endhighlight %}
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### Related Statements
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- [ALTER VIEW](sql-ref-syntax-ddl-alter-view.md)
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- [DROP VIEW](sql-ref-syntax-ddl-drop-view.md)
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