cloud-fan commented on code in PR #40811:
URL: https://github.com/apache/spark/pull/40811#discussion_r1170717475
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sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/subquery.scala:
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@@ -254,13 +254,20 @@ object SubExprUtils extends PredicateHelper {
* scalar subquery during planning.
*
* Note: `exprId` is used to have a unique name in explain string output.
+ *
+ * `mayHaveCountBug` is whether it's possible for the subquery to evaluate to
non-null on
+ * empty input (zero tuples). It is false if the subquery has a GROUP BY
clause, because in that
+ * case the subquery yields no row at all on empty input to the GROUP BY,
which evaluates to NULL.
+ * It is set in PullupCorrelatedPredicates to true/false, before it is set its
value is None.
+ * See constructLeftJoins in RewriteCorrelatedScalarSubquery for more details.
*/
case class ScalarSubquery(
plan: LogicalPlan,
outerAttrs: Seq[Expression] = Seq.empty,
exprId: ExprId = NamedExpression.newExprId,
joinCond: Seq[Expression] = Seq.empty,
- hint: Option[HintInfo] = None)
+ hint: Option[HintInfo] = None,
+ mayHaveCountBug: Option[Boolean] = None)
Review Comment:
how about we make the naming easier to understand? `hasGlobalAggregate`?
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