From 6274092992b1f5fe8d5949fcc6e58d0cb0a3b79e Mon Sep 17 00:00:00 2001
From: TJ Banghart <tjbanghart@gmail.com>
Date: Fri, 22 Nov 2024 13:50:40 -0800
Subject: [PATCH] [CALCITE-6688] Allow basic symmetric operators to be
 reversed.

---
 .../java/org/apache/calcite/sql/SqlBasicFunction.java     | 4 ++++
 .../java/org/apache/calcite/rex/RexNormalizeTest.java     | 8 ++++++++
 .../org/apache/calcite/rex/RexProgramBuilderBase.java     | 8 ++++++++
 3 files changed, 20 insertions(+)

diff --git a/core/src/main/java/org/apache/calcite/sql/SqlBasicFunction.java b/core/src/main/java/org/apache/calcite/sql/SqlBasicFunction.java
index 980df24d4e8..4885175f593 100644
--- a/core/src/main/java/org/apache/calcite/sql/SqlBasicFunction.java
+++ b/core/src/main/java/org/apache/calcite/sql/SqlBasicFunction.java
@@ -158,6 +158,10 @@ public static SqlBasicFunction create(String name,
   @Override public boolean isDeterministic() {
     return deterministic;
   }
+  
+  @Override public @Nullable SqlOperator reverse() {
+    return isSymmetrical() ? this : null;
+  }
 
   @Override public SqlMonotonicity getMonotonicity(SqlOperatorBinding call) {
     return monotonicityInference.apply(call);
diff --git a/core/src/test/java/org/apache/calcite/rex/RexNormalizeTest.java b/core/src/test/java/org/apache/calcite/rex/RexNormalizeTest.java
index 0939dd16de7..c1827638d63 100644
--- a/core/src/test/java/org/apache/calcite/rex/RexNormalizeTest.java
+++ b/core/src/test/java/org/apache/calcite/rex/RexNormalizeTest.java
@@ -91,6 +91,14 @@ class RexNormalizeTest extends RexProgramTestBase {
     assertNodeEquals(
         ne(vBool(0), vBool(1)),
         ne(vBool(1), vBool(0)));
+
+    assertNodeEquals(
+        greatest(vInt(0), vInt(1)),
+        greatest(vInt(1), vInt(0)));
+
+    assertNodeEquals(
+        least(vInt(0), vInt(1)),
+        least(vInt(1), vInt(0)));
   }
 
   @Test void reversibleDifferentArgOps() {
diff --git a/core/src/test/java/org/apache/calcite/rex/RexProgramBuilderBase.java b/core/src/test/java/org/apache/calcite/rex/RexProgramBuilderBase.java
index f8f98fdfa03..6051e758016 100644
--- a/core/src/test/java/org/apache/calcite/rex/RexProgramBuilderBase.java
+++ b/core/src/test/java/org/apache/calcite/rex/RexProgramBuilderBase.java
@@ -25,6 +25,7 @@
 import org.apache.calcite.rel.type.RelDataTypeFactory;
 import org.apache.calcite.rel.type.RelDataTypeSystem;
 import org.apache.calcite.sql.fun.SqlInternalOperators;
+import org.apache.calcite.sql.fun.SqlLibraryOperators;
 import org.apache.calcite.sql.fun.SqlStdOperatorTable;
 import org.apache.calcite.sql.type.SqlTypeName;
 
@@ -326,6 +327,13 @@ protected RexNode sub(RexNode n1, RexNode n2) {
   protected RexNode add(RexNode n1, RexNode n2) {
     return rexBuilder.makeCall(SqlStdOperatorTable.PLUS, n1, n2);
   }
+  protected RexNode greatest(RexNode... nodes) {
+    return rexBuilder.makeCall(SqlLibraryOperators.GREATEST, nodes);
+  }
+
+  protected RexNode least(RexNode... nodes) {
+    return rexBuilder.makeCall(SqlLibraryOperators.LEAST, nodes);
+  }
 
   protected RexNode m2v(RexNode n) {
     return rexBuilder.makeCall(SqlInternalOperators.M2V, n);