[CALCITE-3852] RexSimplify doesn't simplify NOT EQUAL predicates

core/src/main/java/org/apache/calcite/rex/RexSimplify.java

@@ -1560,18 +1560,55 @@ private <C extends Comparable<C>> RexNode simplifyAnd2ForUnknownAsFalse(
     return RexUtil.composeConjunction(rexBuilder, terms);
   }
 
+  private RexNode simplifyNotEqual(RexNode e) {
+    final Comparison comparison = Comparison.of(e);
+    if (comparison == null) {
+      return e;
+    }
+
+    for (RexNode node: predicates.pulledUpPredicates) {
+      final Comparison predicate = Comparison.of(node);
+      if (predicate == null
+          || predicate.kind != SqlKind.EQUALS
+          || !predicate.ref.equals(comparison.ref)) {
+        continue;
+      }
+
+      // Given x=5, x!=5 can be simplified to 'null and x is null' and x!=3 can
+      // be simplified to 'null or x is not null'.
+      RexNode simplified;
+      if (predicate.literal.equals(comparison.literal)) {
+        simplified = rexBuilder.makeCall(SqlStdOperatorTable.AND,
+            rexBuilder.makeNullLiteral(e.getType()),
+            rexBuilder.makeCall(SqlStdOperatorTable.IS_NULL, comparison.ref));
+      } else {
+        simplified = rexBuilder.makeCall(SqlStdOperatorTable.OR,
+            rexBuilder.makeNullLiteral(e.getType()),
+            rexBuilder.makeCall(SqlStdOperatorTable.IS_NOT_NULL, comparison.ref));
+      }
+      return simplify(simplified);
+    }
+
+    return e;
+  }
+
   private <C extends Comparable<C>> RexNode simplifyUsingPredicates(RexNode e,
       Class<C> clazz) {
     if (predicates.pulledUpPredicates.isEmpty()) {
       return e;
     }
+
+    if (e.getKind() == SqlKind.NOT_EQUALS) {
+      return simplifyNotEqual(e);
+    }
+
     final Comparison comparison = Comparison.of(e);
     // Check for comparison with null values
     if (comparison == null
-        || comparison.kind == SqlKind.NOT_EQUALS
         || comparison.literal.getValue() == null) {
       return e;
     }
+
     final C v0 = comparison.literal.getValueAs(clazz);
     final Range<C> range = range(comparison.kind, v0);
     final Range<C> range2 =

core/src/test/java/org/apache/calcite/rex/RexProgramTest.java

@@ -2551,6 +2551,20 @@ private static String getString(ImmutableMap<RexNode, RexNode> map) {
     checkSimplifyFilter(gt(ref, literal(9)), relOptPredicateList, "false");
   }
 
+  @Test public void testSimplifyNotEqual() {
+    RexNode ref = input(tInt(), 0);
+    RelOptPredicateList relOptPredicateList = RelOptPredicateList.of(rexBuilder,
+        ImmutableList.of(eq(ref, literal(9))));
+    checkSimplifyFilter(ne(ref, literal(9)), relOptPredicateList, "false");
+    checkSimplifyFilter(ne(ref, literal(5)), relOptPredicateList, "true");
+
+    ref = input(tInt(true), 0);
+    checkSimplifyFilter(ne(ref, literal(9)), relOptPredicateList,
+        "AND(null, IS NULL($0))");
+    checkSimplifyFilter(ne(ref, literal(5)), relOptPredicateList,
+        "OR(null, IS NOT NULL($0))");
+  }
+
   @Test public void testSimplifyNonDeterministicFunction() {
     final SqlOperator ndc = new SqlSpecialOperator(
         "NDC",

core/src/test/java/org/apache/calcite/test/MaterializationTest.java

@@ -1208,7 +1208,7 @@ private static void checkNoMaterialize_(String materialize, String query,
                     SqlStdOperatorTable.AND,
                     i0_eq_0,
                     i1_eq_1)));
-    checkSatisfiable(e6, "AND(=($0, 0), OR(<>($0, 0), <>($1, 1)))");
+    checkSatisfiable(e6, "AND(=($0, 0), <>($1, 1))");
 
     // "$0 = 0 AND ($1 = 1 AND NOT ($0 = 0))" is not satisfiable.
     final RexNode e7 =

core/src/test/resources/org/apache/calcite/test/RelOptRulesTest.xml

@@ -152,7 +152,7 @@ where case when (sal = 1000) then
         <Resource name="planAfter">
             <![CDATA[
 LogicalProject(SAL=[$5])
-  LogicalFilter(condition=[OR(=($5, 1000), AND(=($5, 2000), <>($5, 1000)))])
+  LogicalFilter(condition=[OR(=($5, 1000), =($5, 2000))])
     LogicalTableScan(table=[[CATALOG, SALES, EMP]])
 ]]>
         </Resource>