[GitHub] [druid] abhishekrb19 commented on a diff in pull request #14441: Improvements to `EXPLAIN PLAN` attributes

["abhishekrb19 (via GitHub)" <gi...@apache.org>]

abhishekrb19 commented on code in PR #14441:
URL: https://github.com/apache/druid/pull/14441#discussion_r1241009757


##########
sql/src/main/java/org/apache/druid/sql/calcite/parser/DruidSqlParserUtils.java:
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@@ -302,6 +309,82 @@ public static SqlOrderBy convertClusterByToOrderBy(SqlNode query, SqlNodeList cl
     );
   }
 
+  /**
+   * Return resolved clustered by columns specified to output columns.
+   * For example,
+   * EXPLAIN PLAN FOR
+   * INSERT INTO w000
+   * SELECT
+   *  TIME_PARSE("timestamp") AS __time,
+   *  page AS page_alias,
+   *  FLOOR("cost"),
+   *  country,
+   *  citName
+   * FROM ...
+   * PARTITIONED BY DAY
+   * CLUSTERED BY 1, 2, 3, cityName
+   *
+   * The above SQL will return the following clusteredBy columns: ["__time", "page_alias", "FLOOR(\"cost\")", cityName"]
+   * Any ordinal and expression specified in the CLUSTERED BY clause will resolve to the final output column name.
+   * @param clusteredByNodes  List of {@link SqlNode}s representing columns to be clustered by.
+   * @param sourceNode The select or order by source node.
+   */
+  @Nullable
+  public static List<String> resolveClusteredByColumnsToOutputColumns(SqlNodeList clusteredByNodes, SqlNode sourceNode)
+  {
+    // CLUSTERED BY is an optional clause
+    if (clusteredByNodes == null) {
+      return null;
+    }
+
+    Preconditions.checkArgument(sourceNode instanceof SqlOrderBy || sourceNode instanceof SqlSelect,

Review Comment:
   This is basically where the output names can be extracted from: [SqlSelect](https://calcite.apache.org/javadocAggregate/org/apache/calcite/sql/SqlSelect.html) projections or `SqlOrderBy` since we convert them [here](https://github.com/apache/druid/blob/master/sql/src/main/java/org/apache/druid/sql/calcite/parser/DruidSqlParserUtils.java#L278)



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