[SPARK-33884][SQL] Simplify CaseWhenclauses with (true and false) and (false and true)

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

@@ -486,6 +486,11 @@ object SimplifyConditionals extends Rule[LogicalPlan] with PredicateHelper {
       case If(cond, FalseLiteral, l @ Literal(null, _)) if !cond.nullable => And(Not(cond), l)
       case If(cond, TrueLiteral, l @ Literal(null, _)) if !cond.nullable => Or(cond, l)
 
+      case CaseWhen(Seq((cond, TrueLiteral)), Some(FalseLiteral)) =>
+        if (cond.nullable) EqualNullSafe(cond, TrueLiteral) else cond
+      case CaseWhen(Seq((cond, FalseLiteral)), Some(TrueLiteral)) =>
+        if (cond.nullable) Not(EqualNullSafe(cond, TrueLiteral)) else Not(cond)
+
       case e @ CaseWhen(branches, elseValue) if branches.exists(x => falseOrNullLiteral(x._1)) =>
         // If there are branches that are always false, remove them.
         // If there are no more branches left, just use the else value.

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/PushFoldableIntoBranchesSuite.scala

@@ -141,7 +141,7 @@ class PushFoldableIntoBranchesSuite
       CaseWhen(Seq((LessThan(Rand(1), Literal(0.5)), Literal(1))), Some(Literal(2)))
     assert(!nonDeterministic.deterministic)
     assertEquivalent(EqualTo(nonDeterministic, Literal(2)),
-      CaseWhen(Seq((LessThan(Rand(1), Literal(0.5)), FalseLiteral)), Some(TrueLiteral)))
+      GreaterThanOrEqual(Rand(1), Literal(0.5)))
     assertEquivalent(EqualTo(nonDeterministic, Literal(3)),
       CaseWhen(Seq((LessThan(Rand(1), Literal(0.5)), FalseLiteral)), Some(FalseLiteral)))
 
@@ -269,4 +269,13 @@ class PushFoldableIntoBranchesSuite
         Literal.create(null, BooleanType))
     }
   }
+
+  test("SPARK-33884: simplify CaseWhen clauses with (true and false) and (false and true)") {
+    assertEquivalent(
+      EqualTo(CaseWhen(Seq(('a > 10, Literal(0))), Literal(1)), Literal(0)),
+      'a > 10 <=> TrueLiteral)
+    assertEquivalent(
+      EqualTo(CaseWhen(Seq(('a > 10, Literal(0))), Literal(1)), Literal(1)),
+      Not('a > 10 <=> TrueLiteral))
+  }
 }

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/SimplifyConditionalSuite.scala

@@ -243,4 +243,40 @@ class SimplifyConditionalSuite extends PlanTest with ExpressionEvalHelper with P
         Literal.create(null, IntegerType))
     }
   }
+
+  test("SPARK-33884: simplify CaseWhen clauses with (true and false) and (false and true)") {
+    // verify the boolean equivalence of all transformations involved
+    val fields = Seq(
+      'cond.boolean.notNull,
+      'cond_nullable.boolean,
+      'a.boolean,
+      'b.boolean
+    )
+    val Seq(cond, cond_nullable, a, b) = fields.zipWithIndex.map { case (f, i) => f.at(i) }
+
+    val exprs = Seq(
+      // actual expressions of the transformations: original -> transformed
+      CaseWhen(Seq((cond, TrueLiteral)), FalseLiteral) -> cond,
+      CaseWhen(Seq((cond, FalseLiteral)), TrueLiteral) -> !cond,
+      CaseWhen(Seq((cond_nullable, TrueLiteral)), FalseLiteral) -> (cond_nullable <=> true),
+      CaseWhen(Seq((cond_nullable, FalseLiteral)), TrueLiteral) -> (!(cond_nullable <=> true)))
+
+    // check plans
+    for ((originalExpr, expectedExpr) <- exprs) {
+      assertEquivalent(originalExpr, expectedExpr)
+    }
+
+    // check evaluation
+    val binaryBooleanValues = Seq(true, false)
+    val ternaryBooleanValues = Seq(true, false, null)
+    for (condVal <- binaryBooleanValues;
+         condNullableVal <- ternaryBooleanValues;
+         aVal <- ternaryBooleanValues;
+         bVal <- ternaryBooleanValues;
+         (originalExpr, expectedExpr) <- exprs) {
+      val inputRow = create_row(condVal, condNullableVal, aVal, bVal)
+      val optimizedVal = evaluateWithoutCodegen(expectedExpr, inputRow)
+      checkEvaluation(originalExpr, optimizedVal, inputRow)
+    }
+  }
 }