[GitHub] [spark] wangyum commented on a diff in pull request #42129: [SPARK-44527][SQL] Replace ScalarSubquery with null if its maxRows is 0

["wangyum (via GitHub)" <gi...@apache.org>]

wangyum commented on code in PR #42129:
URL: https://github.com/apache/spark/pull/42129#discussion_r1275885210


##########
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/expressions.scala:
##########
@@ -529,6 +530,15 @@ object SimplifyBinaryComparison
         case TrueLiteral EqualNullSafe b if !b.nullable => b
         case a EqualNullSafe FalseLiteral if !a.nullable => Not(a)
         case FalseLiteral EqualNullSafe b if !b.nullable => Not(b)
+
+        case EqualNullSafe(a: ScalarSubquery, b: ScalarSubquery)
+            if a.plan.maxRows.contains(0) && b.plan.maxRows.contains(0) =>
+          TrueLiteral
+        case e: EqualNullSafe => e
+        case BinaryComparison(a: ScalarSubquery, _) if a.plan.maxRows.contains(0) =>
+          Literal(null, BooleanType)

Review Comment:
   Should move it to `ConstantFolding `.



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