From 56a02eaaa63f297d3dbaf0ca183e4248d4882834 Mon Sep 17 00:00:00 2001
From: Yuming Wang <yumwang@ebay.com>
Date: Wed, 14 Nov 2018 10:55:25 +0800
Subject: [PATCH] Enhance LikeSimplification

---
 .../sql/catalyst/optimizer/expressions.scala  | 13 +++++++++++
 .../optimizer/LikeSimplificationSuite.scala   | 23 +++++++++++++++++--
 2 files changed, 34 insertions(+), 2 deletions(-)

diff --git a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/expressions.scala b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/expressions.scala
index 2b29b49d00ab9..da705046c8c42 100644
--- a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/expressions.scala
+++ b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/expressions.scala
@@ -504,6 +504,19 @@ object LikeSimplification extends Rule[LogicalPlan] {
             Like(input, Literal.create(pattern, StringType))
         }
       }
+
+    case Like(Literal(pattern, StringType), input) =>
+      if (pattern == null) {
+        // If pattern is null, return null value directly, since "null like col" == null.
+        Literal(null, BooleanType)
+      } else {
+        pattern.toString match {
+          case equalTo(str) =>
+            EqualTo(Literal(str), input)
+          case _ =>
+            Like(Literal.create(pattern, StringType), input)
+        }
+      }
   }
 }
 
diff --git a/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/LikeSimplificationSuite.scala b/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/LikeSimplificationSuite.scala
index f64d10357ce2f..763b0c6ea2497 100644
--- a/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/LikeSimplificationSuite.scala
+++ b/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/LikeSimplificationSuite.scala
@@ -88,7 +88,7 @@ class LikeSimplificationSuite extends PlanTest {
     comparePlans(optimized, correctAnswer)
   }
 
-  test("simplify Like into EqualTo") {
+  test("simplify Like into EqualTo (Like(input, literal) case)") {
     val originalQuery =
       testRelation
         .where(('a like "") || ('a like "abc"))
@@ -101,9 +101,28 @@ class LikeSimplificationSuite extends PlanTest {
     comparePlans(optimized, correctAnswer)
   }
 
-  test("null pattern") {
+  test("simplify Like into EqualTo (Like(literal, input) case)") {
+    val originalQuery =
+      testRelation
+        .where(("" like 'a) || ("abc" like 'a))
+
+    val optimized = Optimize.execute(originalQuery.analyze)
+    val correctAnswer = testRelation
+      .where(("" === 'a) || ("abc" === 'a))
+      .analyze
+
+    comparePlans(optimized, correctAnswer)
+  }
+
+  test("null pattern (Like(input, literal) case)") {
     val originalQuery = testRelation.where('a like Literal(null, StringType)).analyze
     val optimized = Optimize.execute(originalQuery)
     comparePlans(optimized, testRelation.where(Literal(null, BooleanType)).analyze)
   }
+
+  test("null pattern (Like(literal, input) case)") {
+    val originalQuery = testRelation.where(Literal(null, StringType) like 'a).analyze
+    val optimized = Optimize.execute(originalQuery)
+    comparePlans(optimized, testRelation.where(Literal(null, BooleanType)).analyze)
+  }
 }