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
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@@ -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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