Jackie-Jiang commented on a change in pull request #4595: Implement all 
transform function APIs for MapValueTransformFunction
URL: https://github.com/apache/incubator-pinot/pull/4595#discussion_r321951994
 
 

 ##########
 File path: 
pinot-core/src/main/java/org/apache/pinot/core/operator/transform/function/MapValueTransformFunction.java
 ##########
 @@ -29,20 +31,25 @@
 
 
 /**
- * map_value(keyColName, 'keyName', valColName)
+ * The MAP_VALUE transform function takes 3 arguments: keyColumn, keyValue, 
valueColumn, where keyColumn and valueColumn
+ * are dictionary-encoded multi-value columns, and keyValue must be a literal 
(number or string). In order to make
+ * MAP_VALUE transform function work, the keyValue provided must exist in the 
keyColumn. To ensure that, the query can
+ * have a filter on the keyColumn, e.g. SELECT mapValue(key, 'myKey', value) 
FROM myTable WHERE key = 'myKey'.
  */
 public class MapValueTransformFunction extends BaseTransformFunction {
+  public static final String FUNCTION_NAME = "mapValue";
 
 Review comment:
   We already have `valueIn`, `timeConvert`, `dateTimeConvert`. Prefer keeping 
them the same way.

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