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From GitBox <...@apache.org>
Subject [GitHub] [flink] KurtYoung commented on a change in pull request #8520: [FLINK-12600] [table-planner-blink] Introduce planner rules to do deterministic rewriting on RelNode
Date Tue, 28 May 2019 06:19:42 GMT
KurtYoung commented on a change in pull request #8520: [FLINK-12600] [table-planner-blink]
Introduce planner rules to do deterministic rewriting on RelNode
URL: https://github.com/apache/flink/pull/8520#discussion_r287943782

 File path: flink-table/flink-table-planner-blink/src/main/scala/org/apache/flink/table/plan/rules/logical/FlinkRewriteSubQueryRule.scala
 @@ -0,0 +1,154 @@
+ * 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.plan.rules.logical
+import org.apache.calcite.plan.RelOptRule.{any, operandJ}
+import org.apache.calcite.plan.{RelOptRule, RelOptRuleCall, RelOptRuleOperand}
+import org.apache.calcite.rel.RelNode
+import org.apache.calcite.rel.core.{Aggregate, Filter, RelFactories}
+import org.apache.calcite.rex.{RexShuttle, _}
+import org.apache.calcite.sql.SqlKind
+import org.apache.calcite.sql.`type`.SqlTypeFamily
+import org.apache.calcite.sql.fun.SqlCountAggFunction
+import org.apache.calcite.tools.RelBuilderFactory
+import scala.collection.JavaConversions._
+  * Planner rule that rewrites filter condition like:
+  * `(select count(*) from T) > 0` to `exists(select * from T)`,
 Review comment:
   I'm confused, the original query is aggregate, but you want to convert it to a semi join,
knowing that the estimation of semi join is not reliable. 
   Take a step back, why semi join is better than aggregate in this case?

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