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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FLINK-7821) Replace Table.limit() by Table.fetch() and Table.offset()
Date Tue, 24 Oct 2017 15:47:01 GMT

    [ https://issues.apache.org/jira/browse/FLINK-7821?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16217124#comment-16217124
] 

ASF GitHub Bot commented on FLINK-7821:
---------------------------------------

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

    https://github.com/apache/flink/pull/4813#discussion_r146605323
  
    --- Diff: docs/dev/table/tableApi.md ---
    @@ -985,19 +985,22 @@ Table result = in.orderBy("a.asc");
     
         <tr>
           <td>
    -        <strong>Limit</strong><br>
    +        <strong>Offset &amp; Fetch</strong><br>
             <span class="label label-primary">Batch</span>
           </td>
           <td>
    -        <p>Similar to a SQL LIMIT clause. Limits a sorted result to a specified
number of records from an offset position. Limit is technically part of the Order By operator
and thus must be preceded by it.</p>
    +        <p>Similar to the SQL OFFSET and FETCH clauses. Offset and Fetch limit
the number of records returned from a sorted result. Offset and Fetch are technically part
of the Order By operator and thus must be preceded by it.</p>
     {% highlight java %}
     Table in = tableEnv.fromDataSet(ds, "a, b, c");
    -Table result = in.orderBy("a.asc").limit(3); // returns unlimited number of records beginning
with the 4th record
    -{% endhighlight %}
    -or
    -{% highlight java %}
    -Table in = tableEnv.fromDataSet(ds, "a, b, c");
    -Table result = in.orderBy("a.asc").limit(3, 5); // returns 5 records beginning with the
4th record
    +
    +// returns the first 5 records from the sorted result
    +Table result1 = in.orderBy("a.asc").fetch(5); 
    +
    +// returns all records beginning with the 4th record from the sorted result
    +Table result2 = in.orderBy("a.asc").offset(3);
    +
    +// returns the first 5 records beginning with the 10th record from the sorted result
    --- End diff --
    
    I think @xccui is right. An offset of 10 means that the first 10 rows are omitted from
the result. 
    Otherwise offset 1 would not offset.
    I'll update the docs.


> Replace Table.limit() by Table.fetch() and Table.offset()
> ---------------------------------------------------------
>
>                 Key: FLINK-7821
>                 URL: https://issues.apache.org/jira/browse/FLINK-7821
>             Project: Flink
>          Issue Type: Improvement
>          Components: Table API & SQL
>    Affects Versions: 1.4.0
>            Reporter: Fabian Hueske
>            Assignee: Fabian Hueske
>            Priority: Minor
>
> The Table API method limit() exists in two variants:
> - {{limit(offset)}} returns all but the first {{offset}} records.
> - {{limit(offset, fetch)}} returns {{fetch}} records starting from the {{offset}}'s record.
> Especially, the behavior of {{limit(offset)}} is confusing because one would rather expect
a behavior of returning the {{offset}} first records instead of all but the {{offset}} first
records.
> Moreover, the only way to return the first {{x}} records is to specify a {{0}} offset
as {{limit(0, x)}}.
> I propose to deprecate and replace both {{limit()}} variants by two new methods {{Table.offset(offset)}}
and {{Table.fetch(fetch)}} that can be combined as follows:
> {code}
> table.orderBy(...).fetch(x)
> table.orderBy(...).offset(x)
> table.orderBy(...).offset(x).fetch(y)
> {code}



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