[ 
https://issues.apache.org/jira/browse/FLINK-3940?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15404137#comment-15404137
 ] 

ASF GitHub Bot commented on FLINK-3940:
---------------------------------------

Github user twalthr commented on a diff in the pull request:

    https://github.com/apache/flink/pull/2282#discussion_r73172351
  
    --- Diff: 
flink-libraries/flink-table/src/main/scala/org/apache/flink/api/table/plan/logical/operators.scala
 ---
    @@ -150,6 +150,47 @@ case class Sort(order: Seq[Ordering], child: 
LogicalNode) extends UnaryNode {
       }
     }
     
    +case class Offset(offset: Int, child: LogicalNode) extends UnaryNode {
    +  override def output: Seq[Attribute] = child.output
    +
    +  override protected[logical] def construct(relBuilder: RelBuilder): 
RelBuilder = {
    +    child.construct(relBuilder)
    +    relBuilder.limit(offset, -1)
    +  }
    +
    +  override def validate(tableEnv: TableEnvironment): LogicalNode = {
    +    if (tableEnv.isInstanceOf[StreamTableEnvironment]) {
    +      throw new TableException(s"Offset on stream tables is currently not 
supported.")
    +    }
    +    if (!child.validate(tableEnv).isInstanceOf[Sort]) {
    --- End diff --
    
    You don't need to call `validate` here. You can check the Expression itself.


> Add support for ORDER BY OFFSET FETCH
> -------------------------------------
>
>                 Key: FLINK-3940
>                 URL: https://issues.apache.org/jira/browse/FLINK-3940
>             Project: Flink
>          Issue Type: New Feature
>          Components: Table API & SQL
>    Affects Versions: 1.1.0
>            Reporter: Fabian Hueske
>            Assignee: GaoLun
>            Priority: Minor
>
> Currently only ORDER BY without OFFSET and FETCH are supported.
> This issue tracks the effort to add support for OFFSET and FETCH and involves:
> - Implementing the execution strategy in `DataSetSort`
> - adapting the `DataSetSortRule` to support OFFSET and FETCH
> - extending the Table API and validation to support OFFSET and FETCH and 
> generate a corresponding RelNode.



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