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https://issues.apache.org/jira/browse/FLINK-3738?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15241339#comment-15241339
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ASF GitHub Bot commented on FLINK-3738:
---------------------------------------
Github user vasia commented on a diff in the pull request:
https://github.com/apache/flink/pull/1887#discussion_r59735429
--- Diff: docs/apis/batch/libs/table.md ---
@@ -391,9 +375,7 @@ val result = in.distinct();
{% top %}
### Expression Syntax
-Some of operators in previous section expect an expression. These can
either be specified using an embedded Scala DSL or
-a String expression. Please refer to the examples above to learn how
expressions can be
-formulated.
+Some of operators in previous section expect one or more expressions.
Expressions can be specified using an embedded Scala DSL or as Strings. Please
refer to the examples above to learn how expressions can be specified.
--- End diff --
Some of _the_ operators or Some operators
*sections
> Refactor TableEnvironment and TranslationContext
> ------------------------------------------------
>
> Key: FLINK-3738
> URL: https://issues.apache.org/jira/browse/FLINK-3738
> Project: Flink
> Issue Type: Task
> Components: Table API
> Reporter: Fabian Hueske
> Assignee: Fabian Hueske
>
> Currently the TableAPI uses a static object called {{TranslationContext}}
> which holds the Calcite table catalog and a Calcite planner instance.
> Whenever a {{DataSet}} or {{DataStream}} is converted into a {{Table}} or
> registered as a {{Table}} on the {{TableEnvironment}}, a new entry is added
> to the catalog. The first time a {{Table}} is added, a planner instance is
> created. The planner is used to optimize the query (defined by one or more
> Table API operations and/or one ore more SQL queries) when a {{Table}} is
> converted into a {{DataSet}} or {{DataStream}}. Since a planner may only be
> used to optimize a single program, the choice of a single static object is
> problematic.
> I propose to refactor the {{TableEnvironment}} to take over the
> responsibility of holding the catalog and the planner instance.
> - A {{TableEnvironment}} holds a catalog of registered tables and a single
> planner instance.
> - A {{TableEnvironment}} will only allow to translate a single {{Table}}
> (possibly composed of several Table API operations and SQL queries) into a
> {{DataSet}} or {{DataStream}}.
> - A {{TableEnvironment}} is bound to an {{ExecutionEnvironment}} or a
> {{StreamExecutionEnvironment}}. This is necessary to create data source or
> source functions to read external tables or streams.
> - {{DataSet}} and {{DataStream}} need a reference to a {{TableEnvironment}}
> to be converted into a {{Table}}. This will prohibit implicit casts as
> currently supported for the DataSet Scala API.
> - A {{Table}} needs a reference to the {{TableEnvironment}} it is bound to.
> Only tables from the same {{TableEnvironment}} can be processed together.
> - The {{TranslationContext}} will be completely removed.
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