[SPARK-28792][SQL][DOC] Document CREATE DATABASE statement in SQL Reference

# Why are the changes needed?
Currently Spark lacks documentation on the supported SQL constructs causing
confusion among users who sometimes have to look at the code to understand the
usage. This is aimed at addressing this issue.

## How was this patch tested?
This is just a documentation change, verified manually.

Author: sharangk

docs/sql-ref-syntax-ddl-create-database.md

@@ -20,38 +20,57 @@ license: |
 ---
 
 ### Description
-Creates a database with the given name. If database with the same name exists an exception will be thrown.
+Creates a database with the specified name. If database with the same name already exists, an exception will be thrown.
 
 ### Syntax
 {% highlight sql %}
-CREATE (DATABASE|SCHEMA) [IF NOT EXISTS] database_name
-  [COMMENT database_comment]
-  [LOCATION database_directory]
-  [WITH DBPROPERTIES (property_name=property_value, ...)]
-
+CREATE {DATABASE | SCHEMA} [ IF NOT EXISTS ] database_name
+  [ COMMENT database_comment ]
+  [ LOCATION database_directory ]
+  [ WITH DBPROPERTIES (property_name=property_value [ , ...]) ]
 {% endhighlight %}
 
 ### Parameters
-- ##### ***IF NOT EXISTS***:
-Creates a database with the given name if it doesn't exists. If a database with the same name already exists, nothing will happen.
-- ##### ***LOCATION***:
-Path of the file system in which database to be created. If the specified path does not exist in the underlying file system, this command creates a directory with the path.
-- ##### ***COMMENT***:
-Description for the Database.
-- ##### ***WITH DBPROPERTIES***:
-Properties for the database in key-value pair.
+<dl>
+    <dt><code><em>database_name</em></code></dt>
+    <dd>Specifies the name of the database to be created.</dd>
+
+    <dt><code><em>IF NOT EXISTS</em></code></dt>
+    <dd>Creates a database with the given name if it doesn't exists. If a database with the same name already exists, nothing will happen.</dd>
+
+    <dt><code><em>database_directory</em></code></dt>
+    <dd>Path of the file system in which database to be created. If the specified path does not exist in the underlying file system, this command creates a directory with the path. If location is not specified, database will be created in default warehouse directory.</dd>
+
+    <dt><code><em>database_comment</em></code></dt>
+    <dd>Description for the database.</dd>
+
+    <dt><code><em>WITH DBPROPERTIES (property_name=property_value [ , ...])</em></code></dt>
+    <dd>Properties for the database in key-value pair.</dd>
+</dl>
 
 ### Examples
 {% highlight sql %}
 -- Create database `customer_db`. This throws exception if database with name customer_db already exists.
 CREATE DATABASE customer_db;
+
 -- Create database `customer_db` only if database with same name doesn't exist.
 CREATE DATABASE IF NOT EXISTS customer_db;
--- Create database `customer_db` only if database with same name doesn't exist with `Comments`, `Specific Location` and `Database properties`.
+
+-- Create database `customer_db` only if database with same name doesn't exist with `Comments`,`Specific Location` and `Database properties`.
 CREATE DATABASE IF NOT EXISTS customer_db COMMENT 'This is customer database' LOCATION '/user' WITH DBPROPERTIES (ID=001, Name='John');
-{% endhighlight %}
 
+-- Verify that properties are set.
+DESCRIBE DATABASE EXTENDED customer_db;
+   +----------------------------+-----------------------------+
+   | database_description_item  | database_description_value  |
+   +----------------------------+-----------------------------+
+   | Database Name              | customer_db                 |
+   | Description                | This is customer database   |
+   | Location                   | hdfs://hacluster/user       |
+   | Properties                 | ((ID,001), (Name,John))     |
+   +----------------------------+-----------------------------+
+{% endhighlight %}
 
-### Related statements.
+### Related Statements
 - [DESCRIBE DATABASE](sql-ref-syntax-aux-describe-database.html)