Github user hvanhovell commented on a diff in the pull request:
https://github.com/apache/spark/pull/8113#discussion_r36818586
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/aggregate/functions.scala
---
@@ -130,23 +138,36 @@ case class First(child: Expression) extends
AlgebraicAggregate {
private val first = AttributeReference("first", child.dataType)()
- override val bufferAttributes = first :: Nil
+ private val valueSet = AttributeReference("valueSet", BooleanType)()
+
+ override val bufferAttributes = first :: valueSet :: Nil
override val initialValues = Seq(
- /* first = */ Literal.create(null, child.dataType)
+ /* first = */ Literal.create(null, child.dataType),
+ /* valueSet = */ Literal.create(false, BooleanType)
)
override val updateExpressions = Seq(
- /* first = */ If(IsNull(first), child, first)
+ /* first = */ If(valueSet, first, child),
+ /* valueSet = */ If(valueSet, valueSet, Literal.create(true,
BooleanType))
)
override val mergeExpressions = Seq(
- /* first = */ If(IsNull(first.left), first.right, first.left)
+ /* first = */ If(valueSet, first.left, first.right),
+ /* valueSet = */ If(valueSet, valueSet, Literal.create(true,
BooleanType))
--- End diff --
We could for now simplify this to ```Literal.create(true, BooleanType)```.
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