[GitHub] [druid] clintropolis commented on a change in pull request #9429: fix issue when distinct grouping dimensions are optimized into the same virtual column expression

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clintropolis commented on a change in pull request #9429: fix issue when distinct grouping dimensions are optimized into the same virtual column expression
URL: https://github.com/apache/druid/pull/9429#discussion_r385425359
 
 

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 File path: sql/src/main/java/org/apache/druid/sql/calcite/aggregation/DimensionExpression.java
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 @@ -28,6 +28,7 @@
 
 public class DimensionExpression
 {
+  private final String inputDimension;
 
 Review comment:
   Heh, I initially had it named `inputColumn` but changed to `inputDimension` to match the `DimensionSpec` which it creates.
   
   However, since this field _actually_ is only used when creating a `DimensionSpec` when the `DimensionExpression` is for a virtual column, I have renamed the field to `virtualColumn`. When a `DimensionExpression` is a direct access or simple extraction, we use `expression.getSimpleExtraction().toDimensionSpec` to craft the `DimensionSpec` instead, so this field is ignored.
   
   To help clarify this, i collapsed the constructors into a single private constructor and made static methods `DimensionExpression.ofSimpleColumn` and `DimensionExpression.ofVirtualColumn` for creating the two types of `DimensionExpression` we have, as per your other comment, which I think helps clear up usage.

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