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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FLINK-3848) Add ProjectableTableSource interface and translation rule
Date Sat, 26 Nov 2016 13:37:59 GMT

    [ https://issues.apache.org/jira/browse/FLINK-3848?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15697939#comment-15697939
] 

ASF GitHub Bot commented on FLINK-3848:
---------------------------------------

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

    https://github.com/apache/flink/pull/2810#discussion_r89671603
  
    --- Diff: flink-libraries/flink-table/src/main/scala/org/apache/flink/api/table/plan/rules/dataSet/BatchProjectableTableSourceScanRule.scala
---
    @@ -0,0 +1,82 @@
    +/*
    + * Licensed to the Apache Software Foundation (ASF) under one
    + * or more contributor license agreements.  See the NOTICE file
    + * distributed with this work for additional information
    + * regarding copyright ownership.  The ASF licenses this file
    + * to you under the Apache License, Version 2.0 (the
    + * "License"); you may not use this file except in compliance
    + * with the License.  You may obtain a copy of the License at
    + *
    + *     http://www.apache.org/licenses/LICENSE-2.0
    + *
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    + * distributed under the License is distributed on an "AS IS" BASIS,
    + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    + * See the License for the specific language governing permissions and
    + * limitations under the License.
    + */
    +
    +package org.apache.flink.api.table.plan.rules.dataSet
    +
    +import org.apache.calcite.plan.RelOptRule._
    +import org.apache.calcite.plan.volcano.RelSubset
    +import org.apache.calcite.plan.{RelOptRule, RelOptRuleCall, RelOptRuleOperand, RelTraitSet}
    +import org.apache.calcite.rel.RelNode
    +import org.apache.calcite.rel.core.TableScan
    +import org.apache.calcite.rel.logical.LogicalProject
    +import org.apache.flink.api.table.plan.nodes.dataset.{BatchProjectableTableSourceScan,
DataSetConvention}
    +import org.apache.flink.api.table.plan.schema.TableSourceTable
    +import org.apache.flink.api.table.sources.{BatchTableSource, ProjectableTableSource}
    +
    +class BatchProjectableTableSourceScanRule(
    +  operand: RelOptRuleOperand,
    +  description: String) extends RelOptRule(operand, description) {
    +
    +  override def matches(call: RelOptRuleCall): Boolean = {
    +    // check that table scan supports projections
    +    val project: LogicalProject = call.rel(0).asInstanceOf[LogicalProject]
    +    val original: RelNode = project.getInput.asInstanceOf[RelSubset].getOriginal
    +
    +    original match {
    +      case scan: TableScan =>
    --- End diff --
    
    The rule has make sure the first RelNode is `LogicalProject` and the second is `TableScan`,
so I think we do not need to check whether `original` is a `TableScan` again here.


> Add ProjectableTableSource interface and translation rule
> ---------------------------------------------------------
>
>                 Key: FLINK-3848
>                 URL: https://issues.apache.org/jira/browse/FLINK-3848
>             Project: Flink
>          Issue Type: New Feature
>          Components: Table API & SQL
>            Reporter: Fabian Hueske
>            Assignee: Anton Solovev
>
> Add a {{ProjectableTableSource}} interface for {{TableSource}} implementation that support
projection push-down.
> The interface could look as follows
> {code}
> def trait ProjectableTableSource {
>   def setProjection(fields: Array[String]): Unit
> }
> {code}
> In addition we need Calcite rules to push a projection into a TableScan that refers to
a {{ProjectableTableSource}}. We might need to tweak the cost model as well to push the optimizer
in the right direction.
> Moreover, the {{CsvTableSource}} could be extended to implement {{ProjectableTableSource}}.



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