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https://issues.apache.org/jira/browse/FLINK-3848?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15676037#comment-15676037
]
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_r88609838
--- Diff:
flink-libraries/flink-table/src/main/scala/org/apache/flink/api/table/sources/ProjectableTableSource.scala
---
@@ -0,0 +1,32 @@
+/*
+ * 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
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * 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.sources
+
+// TODO FLINK-3848
+/**
+ * Defines a TableSource that can return a projected version of the table.
+ *
+ * @tparam T The return type of the [[TableSource]].
+ */
+trait ProjectableTableSource[T] extends TableSource[T] {
+
+ /** Returns a [[TableSource]] with ability to project fields */
+ def setProjection(fields: Array[Int]): Unit
--- End diff --
I would like the definition of `ProjectableTableSource ` be like this :
https://github.com/fhueske/flink/blob/tableProjectSource/flink-libraries/flink-table/src/main/scala/org/apache/flink/api/table/sources/ProjectableTableSource.scala
The `setProjection` should return a copy TableSource. So the action of
project pushdown won't affect other queries using this TableSource. Considering
this case:
```scala
tEnv.registerTableSource("csvTable", csvTable)
val right = tEnv
.ingest("csvTable")
.select('id as 'rid, 'score)
val table = tEnv
.ingest("csvTable")
.select('id, 'last)
.join(right, 'id == 'rid)
```
> 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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