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Subject [GitHub] [drill] paul-rogers commented on a change in pull request #1974: DRILL-7574: Generalize the projection parser
Date Tue, 18 Feb 2020 19:39:07 GMT
paul-rogers commented on a change in pull request #1974: DRILL-7574: Generalize the projection
parser
URL: https://github.com/apache/drill/pull/1974#discussion_r380891905
 
 

 ##########
 File path: exec/java-exec/src/main/java/org/apache/drill/exec/physical/resultSet/project/RequestedColumn.java
 ##########
 @@ -0,0 +1,137 @@
+/*
+ * 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.physical.resultSet.project;
+
+/**
+ * Plan-time properties of a requested column.Represents
+ * a consolidated view of the set of references to a column.
+ * For example, the project list might contain:<br>
+ * <tt>SELECT columns[4], columns[8]</tt><br>
+ * <tt>SELECT a.b, a.c</tt><br>
+ * <tt>SELECT columns, columns[1]</tt><br>
+ * <tt>SELECT a, a.b</tt><br>
+ * In each case, the same column is referenced in different
+ * forms which are consolidated into this abstraction.
+ * <p>
+ * The resulting information is a "pattern": a form of reference
+ * which which a concrete type can be compatible or not. The project
+ * list does not contain sufficient information to definitively pick
+ * a type; it only excludes certain types.
+ * <p>
+ * Depending on the syntax, we can infer if a column must
+ * be an array or map. This is definitive: though we know that
+ * columns of the form above must be an array or a map,
+ * we cannot know if a simple column reference might refer
+ * to an array or map.
+ *
+ * <h4>Compatibility Rules<h4>
+ *
+ * The pattern given by projection is consistent with certain concrete types
+ * as follows. + means any number of additional qualifiers.
+ * <p>
+ * <table>
+ * <tr><th>Type</th><th>Consistent with</th></tr>
+ * <tr><td>Non-repeated MAP</td>
+ *     <td>{@code a+} {@code a.b+}</td></tr>
+ * <tr><td>Repeated MAP</td>
+ *     <td>{@code a+} {@code a.b+} {@code a[n].b+}</td>></tr>
+ * <tr><td>Non-repeated Scalar</td>
+ *     <td>{@code a}</td></tr>
+ * <tr><td>Repeated Scalar</td>
+ *     <td>{@code a} {@code a[n]}</td></tr>
+ * <tr><td>Non-repeated DICT</td>
+ *     <td>{@code a} {@code a['key']}</td></tr>
+ * <tr><td>Repeated DICT</td>
+ *     <td>{@code a} {@code a[n]} {@code a['key']} {@code a[n]['key']}</td></tr>
 
 Review comment:
   @KazydubB , thanks for checking. It seems that the project operator is making up a null
column since it does not know how to do the actual projection. I'll see how I can incorporate
this additional restriction into the code here.

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