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https://issues.apache.org/jira/browse/DRILL-5538?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16060081#comment-16060081
]
ASF GitHub Bot commented on DRILL-5538:
---------------------------------------
Github user jinfengni commented on a diff in the pull request:
https://github.com/apache/drill/pull/844#discussion_r123631660
--- Diff:
exec/java-exec/src/main/java/org/apache/drill/exec/planner/physical/visitor/TopProjectVisitor.java
---
@@ -0,0 +1,139 @@
+/*
+ * 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.drill.exec.planner.physical.visitor;
+
+import org.apache.calcite.rel.RelNode;
+import org.apache.calcite.rel.core.Project;
+import org.apache.calcite.rel.type.RelDataType;
+import org.apache.calcite.rex.RexBuilder;
+import org.apache.calcite.rex.RexNode;
+import org.apache.calcite.rex.RexUtil;
+import org.apache.calcite.sql.validate.SqlValidatorUtil;
+import org.apache.drill.exec.planner.common.DrillRelOptUtil;
+import org.apache.drill.exec.planner.physical.Prel;
+import org.apache.drill.exec.planner.physical.ProjectPrel;
+import org.apache.drill.exec.planner.physical.ScreenPrel;
+import org.apache.drill.exec.planner.physical.WriterPrel;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+
+/**
+ * Adds non-trivial top project to ensure the final output field names are
preserved.
+ * Is added under the screen or writer operators.
--- End diff --
You may add comments why we need such non-trivial project, due to Calcite's
behavior of ProjectRemoveRule. Also, it might be worth mentioning that the
added Project may not be sitting right under Screen/Writer operator in the
physical plan, as we would add additional Projects, for case likes * column
expansion, or partition by column processing.
> Create TopProject with validatedNodeType after PHYSICAL phase
> --------------------------------------------------------------
>
> Key: DRILL-5538
> URL: https://issues.apache.org/jira/browse/DRILL-5538
> Project: Apache Drill
> Issue Type: Bug
> Components: Query Planning & Optimization
> Affects Versions: 1.10.0
> Reporter: Arina Ielchiieva
> Assignee: Arina Ielchiieva
>
> When [RDBMS storage
> plugin|https://drill.apache.org/docs/rdbms-storage-plugin/] is enabled,
> during query execution certain JDBC rules are added.
> One of the rules is
> [ProjectRemoveRule|https://github.com/apache/drill/blob/master/contrib/storage-jdbc/src/main/java/org/apache/drill/exec/store/jdbc/JdbcStoragePlugin.java#L140].
> Drill also uses this rule but during phases when it considers it useful, for
> example, during LOGICAL and JOIN_PLANNING. On the contrary, storage plugin
> rules are added to any phase of query planning. Thus it results to project
> stage to be removed when actually it is needed.
> Sometimes when ProjectRemoveRule decides that project is trivial and removes
> it, during this stage Drill added column alias or removed implicit columns.
> For example, with RDBMS plugin enabled, alias is not displayed for simple
> query:
> {noformat}
> 0: jdbc:drill:zk=local> create temporary table t as select * from sys.version;
> SLF4J: Failed to load class "org.slf4j.impl.StaticLoggerBinder".
> SLF4J: Defaulting to no-operation (NOP) logger implementation
> SLF4J: See http://www.slf4j.org/codes.html#StaticLoggerBinder for further
> details.
> +-----------+----------------------------+
> | Fragment | Number of records written |
> +-----------+----------------------------+
> | 0_0 | 1 |
> +-----------+----------------------------+
> 1 row selected (0.623 seconds)
> 0: jdbc:drill:zk=local> select version as current_version from t;
> +------------------+
> | version |
> +------------------+
> | 1.11.0-SNAPSHOT |
> +------------------+
> 1 row selected (0.28 seconds)
> {noformat}
> Proposed fix is to move the creating of TopProject with validatedNodeType
> after physical planning is done.
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