[GitHub] [flink] KurtYoung commented on a change in pull request #8585: [FLINK-12690][table-api] Introduce a Planner interface

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KurtYoung commented on a change in pull request #8585:  [FLINK-12690][table-api] Introduce a Planner interface 
URL: https://github.com/apache/flink/pull/8585#discussion_r290999294
 
 

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 File path: flink-table/flink-table-api-java/src/main/java/org/apache/flink/table/operations/ModifyOperation.java
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 @@ -0,0 +1,52 @@
+/*
+ * 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.operations;
+
+import org.apache.flink.annotation.Internal;
+import org.apache.flink.table.api.QueryConfig;
+import org.apache.flink.table.api.TableSchema;
+
+import java.util.List;
+
+/**
+ * A {@link TableOperation} that describes the DML queries such as e.g. INSERT or conversion to a
+ * DataStream.
+ *
+ * <p>A tree of {@link QueryOperation} with a {@link ModifyOperation} on top
+ * represents a runnable query that can be transformed into a graph of
+ * {@link org.apache.flink.streaming.api.transformations.StreamTransformation}
+ * via {@link org.apache.flink.table.planner.Planner#translate(List, QueryConfig)}
+ *
+ * <p>It extends from {@link QueryOperation} to enable applying subsequent
+ * {@link QueryOperation}s on top. In other words it makes it possible to have an output
+ * transformation as a middle step of a relational query. This is not supported yet.
+ *
+ * @see QueryOperation
+ */
+@Internal
+public abstract class ModifyOperation extends QueryOperation {
 
 Review comment:
   I think we should not let this class extends from `QueryOperation`, it makes the class hierarchy hard to understand. There are plenty of ways to achieve goal of applying subsequent `QueryOperation` on it. 

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