[SPARK-35449][SQL][3.1] Only extract common expressions from CaseWhen values if elseValue is set

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/EquivalentExpressions.scala

@@ -128,7 +128,13 @@ class EquivalentExpressions {
       // a subexpression among values doesn't need to be in conditions because no matter which
       // condition is true, it will be evaluated.
       val conditions = c.branches.tail.map(_._1)
-      val values = c.branches.map(_._2) ++ c.elseValue
+      // For an expression to be in all branch values of a CaseWhen statement, it must also be in
+      // the elseValue.
+      val values = if (c.elseValue.nonEmpty) {
+        c.branches.map(_._2) ++ c.elseValue
+      } else {
+        Nil
+      }
       Seq(conditions, values)
     case c: Coalesce => Seq(c.children.tail)
     case _ => Nil

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/expressions/SubexpressionEliminationSuite.scala

@@ -209,7 +209,7 @@ class SubexpressionEliminationSuite extends SparkFunSuite with ExpressionEvalHel
       (GreaterThan(add2, Literal(4)), add1) ::
       (GreaterThan(add2, Literal(5)), add1) :: Nil
 
-    val caseWhenExpr2 = CaseWhen(conditions2, None)
+    val caseWhenExpr2 = CaseWhen(conditions2, add1)
     val equivalence2 = new EquivalentExpressions
     equivalence2.addExprTree(caseWhenExpr2)
 
@@ -309,6 +309,22 @@ class SubexpressionEliminationSuite extends SparkFunSuite with ExpressionEvalHel
       CodeGenerator.compile(code)
     }
   }
+
+  test("SPARK-35499: Subexpressions should only be extracted from CaseWhen values with an "
+    + "elseValue") {
+    val add1 = Add(Literal(1), Literal(2))
+    val add2 = Add(Literal(2), Literal(3))
+    val conditions = (GreaterThan(add1, Literal(3)), add1) ::
+      (GreaterThan(add2, Literal(4)), add1) ::
+      (GreaterThan(add2, Literal(5)), add1) :: Nil
+
+    val caseWhenExpr = CaseWhen(conditions, None)
+    val equivalence = new EquivalentExpressions
+    equivalence.addExprTree(caseWhenExpr)
+
+    // `add1` is not in the elseValue, so we can't extract it from the branches
+    assert(equivalence.getAllEquivalentExprs.count(_.size == 2) == 0)
+  }
 }
 
 case class CodegenFallbackExpression(child: Expression)