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spark-instrumented-optimizer/docs/sql-ref-syntax-aux-show-views.md
Eric Wu a28ed86a38
[SPARK-31113][SQL] Add SHOW VIEWS command 
### What changes were proposed in this pull request?
Previously, user can issue `SHOW TABLES` to get info of both tables and views.
This PR (SPARK-31113) implements `SHOW VIEWS` SQL command similar to HIVE to get views only.(https://cwiki.apache.org/confluence/display/Hive/LanguageManual+DDL#LanguageManualDDL-ShowViews)

**Hive** -- Only show view names
```
hive> SHOW VIEWS;
OK
view_1
view_2
...
```

**Spark(Hive-Compatible)** -- Only show view names, used in tests and `SparkSQLDriver` for CLI applications
```
SHOW VIEWS IN showdb;
view_1
view_2
...
```

**Spark** -- Show more information database/viewName/isTemporary
```
spark-sql> SHOW VIEWS;
userdb	view_1	false
userdb	view_2	false
...
```

### Why are the changes needed?
`SHOW VIEWS` command provides better granularity to only get information of views.

### Does this PR introduce any user-facing change?
Add new `SHOW VIEWS` SQL command

### How was this patch tested?
Add new test `show-views.sql` and pass existing tests

Closes #27897 from Eric5553/ShowViews.

Authored-by: Eric Wu <492960551@qq.com>
Signed-off-by: Dongjoon Hyun <dongjoon@apache.org>
2020-04-07 09:25:01 -07:00

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global SHOW VIEWS SHOW VIEWS Licensed to the Apache Software Foundation (ASF) under one or more contributor license agreements. See the NOTICE file distributed with this work for additional information regarding copyright ownership. The ASF licenses this file to You under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0 Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.

Description

The SHOW VIEWS statement returns all the views for an optionally specified database. Additionally, the output of this statement may be filtered by an optional matching pattern. If no database is specified then the views are returned from the current database. If the specified database is global temporary view database, we will list global temporary views. Note that the command also lists local temporary views regardless of a given database.

Syntax

{% highlight sql %} SHOW VIEWS [ { FROM | IN } database_name ] [ LIKE 'regex_pattern' ] {% endhighlight %}

Parameters

{ FROM | IN } database_name
Specifies the database name from which views are listed.
LIKE regex_pattern
Specifies the regular expression pattern that is used to filter out unwanted views.
  • Except for `*` and `|` character, the pattern works like a regex.
  • `*` alone matches 0 or more characters and `|` is used to separate multiple different regexes, any of which can match.
  • The leading and trailing blanks are trimmed in the input pattern before processing.

Example

{% highlight sql %} -- Create views in different databases, also create global/local temp views. CREATE VIEW sam AS SELECT id, salary FROM employee WHERE name = 'sam'; CREATE VIEW sam1 AS SELECT id, salary FROM employee WHERE name = 'sam1'; CREATE VIEW suj AS SELECT id, salary FROM employee WHERE name = 'suj'; USE userdb; CREATE VIEW user1 AS SELECT id, salary FROM default.employee WHERE name = 'user1'; CREATE VIEW user2 AS SELECT id, salary FROM default.employee WHERE name = 'user2'; USE default; CREATE GLOBAL TEMP VIEW temp1 AS SELECT 1 as col1; CREATE TEMP VIEW temp2 AS SELECT 1 as col1;

-- List all views in default database SHOW VIEWS; +-------------+------------+--------------+--+ | namespace | viewName | isTemporary | +-------------+------------+--------------+--+ | default | sam | false | | default | sam1 | false | | default | suj | false | | | temp2 | true | +-------------+------------+--------------+--+

-- List all views from userdb database SHOW VIEWS FROM userdb; +-------------+------------+--------------+--+ | namespace | viewName | isTemporary | +-------------+------------+--------------+--+ | userdb | user1 | false | | userdb | user2 | false | | | temp2 | true | +-------------+------------+--------------+--+

-- List all views in global temp view database SHOW VIEWS IN global_temp; +-------------+------------+--------------+--+ | namespace | viewName | isTemporary | +-------------+------------+--------------+--+ | global_temp | temp1 | true | | | temp2 | true | +-------------+------------+--------------+--+

-- List all views from default database matching the pattern sam* SHOW VIEWS FROM default LIKE 'sam*'; +-----------+------------+--------------+--+ | namespace | viewName | isTemporary | +-----------+------------+--------------+--+ | default | sam | false | | default | sam1 | false | +-----------+------------+--------------+--+

-- List all views from the current database matching the pattern sam|suj｜temp* SHOW VIEWS LIKE 'sam|suj|temp*'; +-------------+------------+--------------+--+ | namespace | viewName | isTemporary | +-------------+------------+--------------+--+ | default | sam | false | | default | suj | false | | | temp2 | true | +-------------+------------+--------------+--+

{% endhighlight %}

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