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Subject [GitHub] walterddr commented on a change in pull request #6521: [FLINK-5315][table] Adding support for distinct operation for table API on DataStream
Date Wed, 08 Aug 2018 15:24:07 GMT
walterddr commented on a change in pull request #6521: [FLINK-5315][table] Adding support for
distinct operation for table API on DataStream
URL: https://github.com/apache/flink/pull/6521#discussion_r208624881
 
 

 ##########
 File path: flink-libraries/flink-table/src/main/scala/org/apache/flink/table/api/scala/expressionDsl.scala
 ##########
 @@ -214,10 +214,16 @@ trait ImplicitExpressionOperations {
   def varSamp = VarSamp(expr)
 
   /**
-    *  Returns multiset aggregate of a given expression.
+    * Returns multiset aggregate of a given expression.
     */
   def collect = Collect(expr)
 
+  /**
+    * Return a distinct field reference to a given expression
+    * @return
+    */
+  def distinct = DistinctAgg(expr)
 
 Review comment:
   This is the particular places I would like to have 2nd opinion on. I thought of 2 ways
of doing this: 
   1. the way I did, adding distinct in `ExpressionDsl.scala`, and treate `distinct` as a
special Aggregation; separately having a `distinct` method in `AggregationFunction` class
for UDAGG.
   2. adding distinct into `ExpressionParser.scala` and create special prefix / suffix rules
to handle distinct modifier with different expression converter.
   
   I prefer the 1st way, since the 2nd way requires unifying the parsing for both `distinct`
in agg and `distinct` in table. But would like to more opinions.

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