[SPARK-28802][DOC][SQL] Document DESCRIBE DATABASE statement in SQL Reference
### What changes were proposed in this pull request? Document DESCRIBE DATABASE statement in SQL Reference ### Why are the changes needed? To complete the SQL Reference ### Does this PR introduce any user-facing change? Yes #### Before There is no documentation for this command in sql reference #### After ![Screen Shot 2019-09-05 at 12 59 32 PM](https://user-images.githubusercontent.com/7550280/64379235-53aec800-cfe3-11e9-8a51-ea55f0455c47.png) ![Screen Shot 2019-09-05 at 12 59 45 PM](https://user-images.githubusercontent.com/7550280/64379247-58737c00-cfe3-11e9-9a51-f12c5c5bc26a.png) ### How was this patch tested? Used jekyll build and serve to verify Closes #25528 from kevinyu98/sql-ref-describe. Lead-authored-by: Kevin Yu <qyu@us.ibm.com> Co-authored-by: Xiao Li <gatorsmile@gmail.com> Signed-off-by: Xiao Li <gatorsmile@gmail.com>
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@ -18,5 +18,77 @@ license: |
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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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`DESCRIBE DATABASE` statement returns the metadata of an existing database. The metadata information includes database
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name, database comment, and database location on the filesystem. If the optional `EXTENDED` option is specified, it
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returns the basic metadata information along with the database properties. The `DATABASE` and `SCHEMA` are
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interchangeable.
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**This page is under construction**
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### Syntax
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{% highlight sql %}
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{DESC | DESCRIBE} DATABASE [EXTENDED] db_name
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{% endhighlight %}
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### Parameters
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<dl>
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<dt><code><em>db_name</em></code></dt>
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<dd>
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Specifies a name of an existing database or an existing schema in the syetem. If the name does not exist, an
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exception is thrown.
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</dd>
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</dl>
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### Example
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{% highlight sql %}
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-- Create employees DATABASE
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CREATE DATABASE employees COMMENT 'For software companies';
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-- Describe employees DATABASE.
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-- Returns Database Name, Description and Root location of the filesystem
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-- for the employees DATABASE.
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DESCRIBE DATABASE employees;
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+-------------------------+-----------------------------+
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|database_description_item|database_description_value |
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+-------------------------+-----------------------------+
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|Database Name |employees |
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|Description |For software companies |
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|Location |file:/Users/Temp/employees.db|
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+-------------------------+-----------------------------+
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-- Create employees DATABASE
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CREATE DATABASE employees COMMENT 'For software companies';
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-- Alter employees database to set DBPROPERTIES
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ALTER DATABASE employees SET DBPROPERTIES ('Create-by' = 'Kevin', 'Create-date' = '09/01/2019');
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-- Describe employees DATABASE with EXTENDED option to return additional database properties
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DESCRIBE DATABASE EXTENDED employees;
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+-------------------------+---------------------------------------------+
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|database_description_item|database_description_value |
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+-------------------------+---------------------------------------------+
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|Database Name |employees |
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|Description |For software companies |
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|Location |file:/Users/Temp/employees.db |
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|Properties |((Create-by,kevin), (Create-date,09/01/2019))|
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+-------------------------+---------------------------------------------+
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-- Create deployment SCHEMA
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CREATE SCHEMA deployment COMMENT 'Deployment environment';
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-- Describe deployment, the DATABASE and SCHEMA are interchangeable, their meaning are the same.
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DESC DATABASE deployment;
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+-------------------------+------------------------------+
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|database_description_item|database_description_value |
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+-------------------------+------------------------------+
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|Database Name |deployment |
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|Description |Deployment environment |
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|Location |file:/Users/Temp/deployment.db|
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+-------------------------+------------------------------+
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{% endhighlight %}
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### Related Statements
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- [DESCRIBE FUNCTION](sql-ref-syntax-aux-describe-function.html)
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- [DESCRIBE TABLE](sql-ref-syntax-aux-describe-table.html)
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- [DESCRIBE QUERY](sql-ref-syntax-aux-describe-query.html)
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