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Subject [GitHub] fhueske commented on a change in pull request #6606: [FLINK-10163] [sql-client] Support views in SQL Client
Date Fri, 24 Aug 2018 17:10:20 GMT
fhueske commented on a change in pull request #6606: [FLINK-10163] [sql-client] Support views
in SQL Client
URL: https://github.com/apache/flink/pull/6606#discussion_r212621362
 
 

 ##########
 File path: docs/dev/table/sqlClient.md
 ##########
 @@ -459,6 +466,50 @@ Web interface: http://localhost:8081
 
 {% top %}
 
+SQL Views
+---------
+
+Views allow to define virtual tables from SQL queries. The view definition is parsed and
validated immediately. However, the actual execution happens when the view is accessed during
the submission of a general `INSERT INTO` or `SELECT` statement.
+
+Views can either be defined in [environment files](sqlClient.html#environment-files) or within
the CLI session.
+
+The following example shows how to define multiple views in a file:
+
+{% highlight yaml %}
+views:
+  - name: MyRestrictedView
+    query: "SELECT MyField2 FROM MyTableSource"
+  - name: MyComplexView
+    query: >
+      SELECT MyField2 + 42, CAST(MyField1 AS VARCHAR)
+      FROM MyTableSource
+      WHERE MyField2 > 200
+{% endhighlight %}
+
+Similar to table sources and sinks, views defined in a session environment file have highest
precendence.
+
+Views can also be created within a CLI session using the `CREATE VIEW` statement:
+
+{% highlight text %}
+CREATE VIEW MyNewView AS SELECT MyField2 FROM MyTableSource
+{% endhighlight %}
+
+The `SHOW VIEW` statement allows for printing a previously created view again:
 
 Review comment:
   I think the way that these commands work is a bit inconsistent with the `SHOW TABLES`,
`SHOW FUNCTIONS`, and `DESCRIBE xxx` commands.
   
   1. Views are listed as regular tables when calling `SHOW TABLES`. 
     * List tables and views together, but mark views as views
     * Or add a `SHOW VIEWS` to only list views (and only list tables with `LIST TABLES`)
   
   2. The schema of a view is returned with `DESCRIBE xxx`. This is fine, but IMO, we should
also return the query. Showing schema and query with different commands is not intuitive to
me.

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