Github user rxin commented on a diff in the pull request: https://github.com/apache/spark/pull/737#discussion_r12546858 --- Diff: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/aggregates.scala --- @@ -166,10 +167,48 @@ case class CountDistinct(expressions: Seq[Expression]) extends AggregateExpressi override def references = expressions.flatMap(_.references).toSet override def nullable = false override def dataType = IntegerType - override def toString = s"COUNT(DISTINCT ${expressions.mkString(",")}})" + override def toString = s"COUNT(DISTINCT ${expressions.mkString(",")})" override def newInstance() = new CountDistinctFunction(expressions, this) } +case class ApproxCountDistinctPartition(child: Expression) + extends AggregateExpression with trees.UnaryNode[Expression] { + override def references = child.references + override def nullable = false + override def dataType = child.dataType + override def toString = s"APPROXIMATE COUNT(DISTINCT $child)" + override def newInstance() = new ApproxCountDistinctPartitionFunction(child, this) +} + +case class ApproxCountDistinctMerge(child: Expression) + extends AggregateExpression with trees.UnaryNode[Expression] { + override def references = child.references + override def nullable = false + override def dataType = IntegerType + override def toString = s"APPROXIMATE COUNT(DISTINCT $child)" + override def newInstance() = new ApproxCountDistinctMergeFunction(child, this) +} + +object ApproxCountDistinct { + val RelativeSD = 0.05 +} + +case class ApproxCountDistinct(child: Expression) + extends PartialAggregate with trees.UnaryNode[Expression] { + override def references = child.references + override def nullable = false + override def dataType = IntegerType + override def toString = s"APPROXIMATE COUNT(DISTINCT $child)" + + override def asPartial: SplitEvaluation = { + val partialCount = Alias(ApproxCountDistinctPartition(child), + "PartialApproxCountDistinct")() --- End diff -- style feedback: just indent this line using 2 spaces instead of aligning them.
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