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https://issues.apache.org/jira/browse/FLINK-5266?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15735523#comment-15735523
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ASF GitHub Bot commented on FLINK-5266:
---------------------------------------
Github user KurtYoung commented on a diff in the pull request:
https://github.com/apache/flink/pull/2961#discussion_r91729382
--- Diff:
flink-libraries/flink-table/src/main/scala/org/apache/flink/api/table/table.scala
---
@@ -881,24 +883,21 @@ class GroupWindowedTable(
* }}}
*/
def select(fields: Expression*): Table = {
--- End diff --
What if user use a customized watermark extracter which used some fields
from the element. For example, we have original table source containing 4
fields: a, b, c, d. And user used "a" field to extract the timestamp and
watermark. But in the later query on the table, only "b" and "c" are used. And
if we do a projection on "b" and "c", and the projection is pushed into table
source further, we will not get field "a" which used to produce timestamp
anymore.
> Eagerly project unused fields when selecting aggregation fields
> ---------------------------------------------------------------
>
> Key: FLINK-5266
> URL: https://issues.apache.org/jira/browse/FLINK-5266
> Project: Flink
> Issue Type: Improvement
> Components: Table API & SQL
> Reporter: Kurt Young
> Assignee: Kurt Young
>
> When we call table's {{select}} method and if it contains some aggregations,
> we will project fields after the aggregation. Would be better to project
> unused fields before the aggregation, and can furthermore leave the
> opportunity to push the project into scan.
> For example, the current logical plan of a simple query:
> {code}
> table.select('a.sum as 's, 'a.max)
> {code}
> is
> {code}
> LogicalProject(s=[$0], TMP_2=[$1])
> LogicalAggregate(group=[{}], TMP_0=[SUM($5)], TMP_1=[MAX($5)])
> LogicalTableScan(table=[[supplier]])
> {code}
> Would be better if we can project unused fields right after scan, and looks
> like this:
> {code}
> LogicalProject(s=[$0], EXPR$1=[$0])
> LogicalAggregate(group=[{}], EXPR$1=[SUM($0)])
> LogicalProject(a=[$5])
> LogicalTableScan(table=[[supplier]])
> {code}
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