[FLINK-17635][docs][table] Add documentation about view support

This closes apache#12502

docs/dev/table/sql/create.md

@@ -31,6 +31,7 @@ Flink SQL supports the following CREATE statements for now:
 
 - CREATE TABLE
 - CREATE DATABASE
+- CREATE VIEW
 - CREATE FUNCTION
 
 ## Run a CREATE statement
@@ -351,6 +352,25 @@ The key and value of expression `key1=val1` should both be string literal.
 
 {% top %}
 
+## CREATE VIEW
+{% highlight sql %}
+CREATE [TEMPORARY] VIEW [IF NOT EXISTS] [catalog_name.][db_name.]view_name
+  [{columnName [, columnName ]* }] [COMMENT view_comment]
+  AS query_expression
+{% endhighlight %}
+
+Create a view with the given query expression. If a view with the same name already exists in the catalog, an exception is thrown.
+
+**TEMPORARY**
+
+Create temporary view that has catalog and database namespaces and overrides views.
+
+**IF NOT EXISTS**
+
+If the view already exists, nothing happens.
+
+{% top %}
+
 ## CREATE FUNCTION
 {% highlight sql%}
 CREATE [TEMPORARY|TEMPORARY SYSTEM] FUNCTION 

docs/dev/table/sql/create.zh.md

@@ -31,6 +31,7 @@ CREATE 语句用于向当前或指定的 [Catalog]({{ site.baseurl }}/zh/dev/tab
 
 - CREATE TABLE
 - CREATE DATABASE
+- CREATE VIEW
 - CREATE FUNCTION
 
 ## 执行 CREATE 语句
@@ -344,6 +345,25 @@ CREATE DATABASE [IF NOT EXISTS] [catalog_name.]db_name
 
 {% top %}
 
+## CREATE VIEW
+{% highlight sql %}
+CREATE [TEMPORARY] VIEW [IF NOT EXISTS] [catalog_name.][db_name.]view_name
+  [{columnName [, columnName ]* }] [COMMENT view_comment]
+  AS query_expression
+{% endhighlight %}
+
+根据给定的 query 语句创建一个视图。若数据库中已经存在同名视图会抛出异常.
+
+**TEMPORARY**
+
+创建一个有 catalog 和数据库命名空间的临时视图，并覆盖原有的视图。
+
+**IF NOT EXISTS**
+
+若该视图已经存在，则不会进行任何操作。
+
+{% top %}
+
 ## CREATE FUNCTION
 {% highlight sql%}
 CREATE [TEMPORARY|TEMPORARY SYSTEM] FUNCTION

docs/dev/table/sql/drop.md

@@ -31,6 +31,7 @@ Flink SQL supports the following DROP statements for now:
 
 - DROP TABLE
 - DROP DATABASE
+- DROP VIEW
 - DROP FUNCTION
 
 ## Run a DROP statement
@@ -143,6 +144,25 @@ Dropping a non-empty database triggers an exception. Enabled by default.
 
 Dropping a non-empty database also drops all associated tables and functions.
 
+## DROP VIEW
+
+{% highlight sql %}
+DROP [TEMPORARY] VIEW  [IF EXISTS] [catalog_name.][db_name.]view_name
+{% endhighlight %}
+
+Drop a view that has catalog and database namespaces. If the view to drop does not exist, an exception is thrown.
+
+**TEMPORARY**
+
+Drop temporary view that has catalog and database namespaces.
+
+**IF EXISTS**
+
+If the view does not exist, nothing happens.
+
+**MAINTAIN DEPENDENCIES**
+Flink does not maintain dependencies of view by CASCADE/RESTRICT keywords, the current way is producing postpone error message when user tries to use the view under the scenarios like the underlying table of view has been dropped.
+
 ## DROP FUNCTION
 
 {% highlight sql%}

docs/dev/table/sql/drop.zh.md

@@ -31,6 +31,7 @@ Flink SQL 目前支持以下 DROP 语句：
 
 - DROP TABLE
 - DROP DATABASE
+- DROP VIEW
 - DROP FUNCTION
 
 ## 执行 DROP 语句
@@ -143,6 +144,25 @@ DROP DATABASE [IF EXISTS] [catalog_name.]db_name [ (RESTRICT | CASCADE) ]
 
 删除一个非空数据库时，把相关联的表与函数一并删除。
 
+## DROP VIEW
+
+{% highlight sql %}
+DROP [TEMPORARY] VIEW  [IF EXISTS] [catalog_name.][db_name.]view_name
+{% endhighlight %}
+
+删除一个有 catalog 和数据库命名空间的视图。若需要删除的视图不存在，则会产生异常。
+
+**TEMPORARY**
+
+删除一个有 catalog 和数据库命名空间的临时视图。
+
+**IF EXISTS**
+
+若视图不存在，则不会进行任何操作。
+
+**依赖管理**
+Flink 没有使用 CASCADE / RESTRICT 关键字来维护视图的依赖关系，当前的方案是在用户使用视图时再提示错误信息，比如在视图的底层表已经被删除等场景。
+
 ## DROP FUNCTION
 
 {% highlight sql%}

docs/dev/table/sql/index.md

@@ -29,8 +29,8 @@ This page describes the SQL language supported in Flink, including Data Definiti
 This page lists all the supported statements supported in Flink SQL for now:
 
 - [SELECT (Queries)](queries.html)
-- [CREATE TABLE, DATABASE, FUNCTION](create.html)
-- [DROP TABLE, DATABASE, FUNCTION](drop.html)
+- [CREATE TABLE, DATABASE, VIEW, FUNCTION](create.html)
+- [DROP TABLE, DATABASE, VIEW, FUNCTION](drop.html)
 - [ALTER TABLE, DATABASE, FUNCTION](alter.html)
 - [INSERT](insert.html)
 - [SQL HINTS](hints.html)

docs/dev/table/sql/index.zh.md

@@ -29,8 +29,8 @@ under the License.
 本页面列出了目前 Flink SQL 所支持的所有语句：
 
 - [SELECT (查询)](queries.html)
-- [CREATE TABLE, DATABASE, FUNCTION](create.html)
-- [DROP TABLE, DATABASE, FUNCTION](drop.html)
+- [CREATE TABLE, DATABASE, VIEW, FUNCTION](create.html)
+- [DROP TABLE, DATABASE, VIEW, FUNCTION](drop.html)
 - [ALTER TABLE, DATABASE, FUNCTION](alter.html)
 - [INSERT](insert.html)
 - [SQL HINTS](hints.html)

docs/dev/table/sql/queries.md

@@ -294,7 +294,7 @@ String literals must be enclosed in single quotes (e.g., `SELECT 'Hello World'`)
 
 ## Operations
 
-### Show and Use
+### Show, Describe, and Use
 
 <div markdown="1">
 <table class="table table-bordered">
@@ -322,9 +322,29 @@ SHOW DATABASES;
 		<p>Show all tables in the current database in the current catalog</p>
 {% highlight sql %}
 SHOW TABLES;
+{% endhighlight %}
+        <p>Show all views in the current database in the current catalog</p>
+{% highlight sql %}
+SHOW VIEWS;
 {% endhighlight %}
       </td>
     </tr>
+    <tr>
+      <td>
+        <strong>Describe</strong><br>
+        <span class="label label-primary">Batch</span> <span class="label label-primary">Streaming</span>
+      </td>
+      <td>
+			<p>Describe the schema of the given table.</p>
+{% highlight sql %}
+DESCRIBE myTable;
+{% endhighlight %}
+            <p>Describe the schema of the given view.</p>
+{% highlight sql %}
+DESCRIBE myView;
+{% endhighlight %}
+      </td>
+    </tr>    
     <tr>
       <td>
         <strong>Use</strong><br>

docs/dev/table/sql/queries.zh.md

@@ -294,7 +294,7 @@ Flink SQL 对于标识符（表、属性、函数名）有类似于 Java 的词
 
 ## 操作符
 
-### Show 与 Use
+### Show, Describe 与 Use
 
 <div markdown="1">
 <table class="table table-bordered">
@@ -322,9 +322,29 @@ SHOW DATABASES;
     <p>显示当前数据库、Catalog中的所有表</p>
 {% highlight sql %}
 SHOW TABLES;
+{% endhighlight %}
+        <p>显示当前数据库、Catalog中的所有视图</p>
+{% highlight sql %}
+SHOW VIEWS;
 {% endhighlight %}
       </td>
     </tr>
+    <tr>
+      <td>
+        <strong>Describe</strong><br>
+        <span class="label label-primary">批处理</span> <span class="label label-primary">流处理</span>
+      </td>
+      <td>
+			<p>描述给定表的 Schema</p>
+{% highlight sql %}
+DESCRIBE myTable;
+{% endhighlight %}
+            <p>描述给定视图的 Schema</p>
+{% highlight sql %}
+DESCRIBE myView;
+{% endhighlight %}
+      </td>
+    </tr>    
     <tr>
       <td>
         <strong>Use</strong><br>