From 2376a3a743d2ece3f81aee881b2fc381803def47 Mon Sep 17 00:00:00 2001
From: NobiGo <nobigogle@gmail.com>
Date: Wed, 16 Feb 2022 14:41:03 +0800
Subject: [PATCH] [CALCITE-4912] Confusing javadoc of RexSimplify.simplify

---
 .../src/main/java/org/apache/calcite/rex/RexSimplify.java | 4 ++--
 .../test/java/org/apache/calcite/rex/RexProgramTest.java  | 8 ++++++--
 2 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/core/src/main/java/org/apache/calcite/rex/RexSimplify.java b/core/src/main/java/org/apache/calcite/rex/RexSimplify.java
index 7c0aa6bb3138..8dd53a985888 100644
--- a/core/src/main/java/org/apache/calcite/rex/RexSimplify.java
+++ b/core/src/main/java/org/apache/calcite/rex/RexSimplify.java
@@ -204,8 +204,8 @@ public RexNode simplifyPreservingType(RexNode e, RexUnknownAs unknownAs,
    *
    * <p>In particular:</p>
    * <ul>
-   * <li>{@code simplify(x = 1 AND y = 2 AND NOT x = 1)}
-   * returns {@code y = 2}</li>
+   * <li>{@code simplify(x = 1 OR NOT x = 1 OR x IS NULL)}
+   * returns {@code TRUE}</li>
    * <li>{@code simplify(x = 1 AND FALSE)}
    * returns {@code FALSE}</li>
    * </ul>
diff --git a/core/src/test/java/org/apache/calcite/rex/RexProgramTest.java b/core/src/test/java/org/apache/calcite/rex/RexProgramTest.java
index 691c9541e5fd..7f68dec914ca 100644
--- a/core/src/test/java/org/apache/calcite/rex/RexProgramTest.java
+++ b/core/src/test/java/org/apache/calcite/rex/RexProgramTest.java
@@ -1003,6 +1003,10 @@ private void checkExponentialCnf(int n) {
         "false", "IS NULL(?0.i)");
     checkSimplifyUnchanged(gt(iRef, hRef));
 
+    // "x = 1 or not x = 1 or x is null" simplifies to "true"
+    checkSimplify(or(eq(hRef, literal(1)), not(eq(hRef, literal(1))), isNull(hRef)), "true");
+    checkSimplify(or(eq(iRef, literal(1)), not(eq(iRef, literal(1))), isNull(iRef)), "true");
+
     // "(not x) is null" to "x is null"
     checkSimplify(isNull(not(vBool())), "IS NULL(?0.bool0)");
     checkSimplify(isNull(not(vBoolNotNull())), "false");
@@ -1130,7 +1134,7 @@ private void checkExponentialCnf(int n) {
     // condition with null value for range
     checkSimplifyFilter(and(gt(aRef, nullBool), ge(bRef, literal(1))), "false");
 
-    // condition "1 < a && 5 < x" yields "5 < x"
+    // condition "1 < a && 5 < a" yields "5 < a"
     checkSimplifyFilter(
         and(lt(literal(1), aRef), lt(literal(5), aRef)),
         RelOptPredicateList.EMPTY,
@@ -1142,7 +1146,7 @@ private void checkExponentialCnf(int n) {
         RelOptPredicateList.EMPTY,
         "SEARCH(?0.a, Sarg[(1..5)])");
 
-    // condition "1 > a && 5 > x" yields "1 > a"
+    // condition "1 > a && 5 > a" yields "1 > a"
     checkSimplifyFilter(
         and(gt(literal(1), aRef), gt(literal(5), aRef)),
         RelOptPredicateList.EMPTY,