[GitHub] [druid] clintropolis commented on a change in pull request #11068: Enable rewriting certain inner joins as filters.

[GitBox <gi...@apache.org>]

clintropolis commented on a change in pull request #11068:
URL: https://github.com/apache/druid/pull/11068#discussion_r608306486



##########
File path: processing/src/main/java/org/apache/druid/query/Queries.java
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@@ -219,4 +224,73 @@
 
     return retVal;
   }
+
+  /**
+   * Helper for implementations of {@link Query#getRequiredColumns()}. Returns the list of columns that will be read
+   * out of a datasource by a query that uses the provided objects in the usual way.
+   *
+   * The returned set always contains {@code __time}, no matter what.
+   *
+   * If the virtual columns, filter, dimensions, aggregators, or additional columns refer to a virtual column, then the
+   * inputs of the virtual column will be returned instead of the name of the virtual column itself. Therefore, the
+   * returned list will never contain the names of any virtual columns.
+   *
+   * @param virtualColumns    virtual columns whose inputs should be included.
+   * @param filter            optional filter whose inputs should be included.
+   * @param dimensions        dimension specs whose inputs should be included.
+   * @param aggregators       aggregators whose inputs should be included.
+   * @param additionalColumns additional columns to include. Each of these will be added to the returned set, unless it
+   *                          refers to a virtual column, in which case the virtual column inputs will be added instead.
+   */
+  public static Set<String> computeRequiredColumns(

Review comment:
       :+1:




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