Github user fhueske commented on a diff in the pull request:
https://github.com/apache/flink/pull/3269#discussion_r101739816
--- Diff:
flink-libraries/flink-table/src/main/scala/org/apache/flink/table/sources/NestedFieldsProjectableTableSource.scala
---
@@ -0,0 +1,39 @@
+/*
+ * 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.table.sources
+
+/**
+ * Adds support for projection push-down to a [[TableSource]] with nested
fields.
+ * A [[TableSource]] extending this interface is able
+ * to project the nested fields of the return table.
+ *
+ * @tparam T The return type of the
[[NestedFieldsProjectableTableSource]].
+ */
+trait NestedFieldsProjectableTableSource[T] extends
ProjectableTableSource[T] {
+
+ /**
+ * Creates a copy of the [[NestedFieldsProjectableTableSource]]
+ * that projects its output on the specified nested fields.
+ *
+ * @param fields The indexes of the fields to return.
+ * @return A copy of the [[NestedFieldsProjectableTableSource]] that
projects its output.
+ */
+ def projectNestedFields(fields: Array[String]):
NestedFieldsProjectableTableSource[T]
--- End diff --
@tonycox, @wuchong: What do you think about changing the signature to
something like:
```
def projectNestedFields(fields: Array[Int], nestedFields:
Array[Array[String]])
```
It would be more aligned with the existing `ProjectableTableSource`
interface.
Both array would need to be of identical size and the String array would
hold the nested fields.
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