richardc-db commented on code in PR #50849:
URL: https://github.com/apache/spark/pull/50849#discussion_r2096557108
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sql/core/src/main/scala/org/apache/spark/sql/execution/ExistingRDD.scala:
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@@ -319,3 +319,51 @@ case class RDDScanExec(
override def getStream: Option[SparkDataStream] = stream
}
+
+/**
+ * A special case of RDDScanExec that is used to represent a scan without a
`FROM` clause.
+ * For example, 'select version()'.
+ *
+ * We do not extend `RDDScanExec` in order to avoid complexity due to
`TreeNode.makeCopy` and
+ * `TreeNode`'s general use of reflection.
+ */
+case class OneRowRelationExec() extends LeafExecNode
+ with StreamSourceAwareSparkPlan
+ with InputRDDCodegen {
+
+ override val nodeName: String = s"Scan OneRowRelation"
+
+ override val output: Seq[Attribute] = Nil
+
+ val rdd = session.sparkContext.parallelize(Seq(InternalRow()), 1)
+
+ override lazy val metrics = Map(
+ "numOutputRows" -> SQLMetrics.createMetric(sparkContext, "number of output
rows"))
+
+ protected override def doExecute(): RDD[InternalRow] = {
+ val numOutputRows = longMetric("numOutputRows")
+ rdd.mapPartitionsWithIndexInternal { (index, iter) =>
+ val proj = UnsafeProjection.create(schema)
+ proj.initialize(index)
+ iter.map { r =>
+ numOutputRows += 1
+ proj(r)
+ }
+ }
+ }
+
+ override def simpleString(maxFields: Int): String = {
+ s"$nodeName${truncatedString(output, "[", ",", "]", maxFields)}"
Review Comment:
the default implementation returns `Scan OneRowRelation`, while the existing
implementation (using RDDScan) returns `Scan OneRowRelation[]`. I figured we
shouldn't change this in the off chance that someone is relying on it.
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