[GitHub] [flink] wuchong commented on a change in pull request #8302: [FLINK-12269][table-blink] Support Temporal Table Join in blink planner and runtime

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wuchong commented on a change in pull request #8302: [FLINK-12269][table-blink] Support Temporal Table Join in blink planner and runtime
URL: https://github.com/apache/flink/pull/8302#discussion_r281491514
 
 

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 File path: flink-table/flink-table-planner-blink/src/main/java/org/apache/flink/table/sources/LookupableTableSource.java
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+/*
+ * 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;
+
+import org.apache.flink.annotation.PublicEvolving;
+import org.apache.flink.table.functions.AsyncTableFunction;
+import org.apache.flink.table.functions.TableFunction;
+
+/**
+ * A {@link TableSource} which supports for lookup accessing via key column(s).
+ * For example, MySQL TableSource can implement this interface to support lookup accessing.
+ * When temporal join this MySQL table, the runtime behavior could be in a lookup fashion.
+ *
+ * @param <T> type of the result
+ */
+@PublicEvolving
+public interface LookupableTableSource<T> extends TableSource<T> {
 
 Review comment:
   Currently, the lookup key of `LookupableTableSource` must be either primary key or index. Therefore, a concrete `LookupableTableSource` should also implement `DefinedIndexes` or `DefinedPrimaryKey`.
   
   > Does this table source support getting lookup function for random keys, even if the columns have no index on them or not the primary key?
   
   No. It will throw exceptions. 

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