francis0407 commented on a change in pull request #24344: [SPARK-27440][SQL]
Optimize uncorrelated predicate subquery
URL: https://github.com/apache/spark/pull/24344#discussion_r278595066
##########
File path:
sql/core/src/main/scala/org/apache/spark/sql/execution/subquery.scala
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@@ -55,6 +55,112 @@ object ExecSubqueryExpression {
}
}
+/**
+ * Exists is used to test for the existence of any record in a subquery.
+ *
+ * This is the physical copy of Exists to be used inside SparkPlan.
+ */
+case class Exists(
+ plan: BaseSubqueryExec,
+ exprId: ExprId)
+ extends ExecSubqueryExpression {
+
+ override def dataType: DataType = BooleanType
+ override def children: Seq[Expression] = Nil
+ override def nullable: Boolean = false
+ override def toString: String =
plan.simpleString(SQLConf.get.maxToStringFields)
+ override def withNewPlan(plan: BaseSubqueryExec): Exists = copy(plan = plan)
+
+ // Whether the subquery returns one or more records
+ @volatile private var result: Boolean = _
+ @volatile private var updated: Boolean = false
+
+ def updateResult(): Unit = {
+ val rows = plan.executeCollect()
+ result = rows.nonEmpty
+ updated = true
+ }
+
+ override def eval(input: InternalRow): Boolean = {
+ require(updated, s"$this has not finished")
+ result
+ }
+
+ override protected def doGenCode(ctx: CodegenContext, ev: ExprCode):
ExprCode = {
+ require(updated, s"$this has not finished")
+ Literal.create(result, BooleanType).doGenCode(ctx, ev)
+ }
+}
+
+/**
+ * Evaluates to `true` if `values` are returned in the subquery's result set.
+ * If `values` are not found in the subquery's result set, and there are nulls
in
+ * `values` or the result set, it should return UNKNOWN.
Review comment:
Yes, NULL is better
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