[SPARK-4513][SQL] Support relational operator '<=>' in Spark SQL

The relational operator '<=>' is not working in Spark SQL. Same works in Spark HiveQL

Author: ravipesala <ravindra.pesala@huawei.com>

Closes #3387 from ravipesala/<=> and squashes the following commits:

7198e90 [ravipesala] Supporting relational operator '<=>' in Spark SQL

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/SparkSQLParser.scala

@@ -61,7 +61,7 @@ class SqlLexical(val keywords: Seq[String]) extends StdLexical {
 
   delimiters += (
     "@", "*", "+", "-", "<", "=", "<>", "!=", "<=", ">=", ">", "/", "(", ")",
-    ",", ";", "%", "{", "}", ":", "[", "]", ".", "&", "|", "^", "~"
+    ",", ";", "%", "{", "}", ":", "[", "]", ".", "&", "|", "^", "~", "<=>"
   )
 
   override lazy val token: Parser[Token] =

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/SqlParser.scala

@@ -234,6 +234,7 @@ class SqlParser extends AbstractSparkSQLParser {
     | termExpression ~ (">=" ~> termExpression) ^^ { case e1 ~ e2 => GreaterThanOrEqual(e1, e2) }
     | termExpression ~ ("!=" ~> termExpression) ^^ { case e1 ~ e2 => Not(EqualTo(e1, e2)) }
     | termExpression ~ ("<>" ~> termExpression) ^^ { case e1 ~ e2 => Not(EqualTo(e1, e2)) }
+    | termExpression ~ ("<=>" ~> termExpression) ^^ { case e1 ~ e2 => EqualNullSafe(e1, e2) }
     | termExpression ~ NOT.? ~ (BETWEEN ~> termExpression) ~ (AND ~> termExpression) ^^ {
         case e ~ not ~ el ~ eu =>
           val betweenExpr: Expression = And(GreaterThanOrEqual(e, el), LessThanOrEqual(e, eu))

sql/core/src/test/scala/org/apache/spark/sql/SQLQuerySuite.scala

@@ -973,4 +973,16 @@ class SQLQuerySuite extends QueryTest with BeforeAndAfterAll {
     checkAnswer(sql("SELECT a.b + 1 FROM data GROUP BY a.b + 1"), 2)
     dropTempTable("data")
   }
+
+  test("Supporting relational operator '<=>' in Spark SQL") {
+    val nullCheckData1 = TestData(1,"1") :: TestData(2,null) :: Nil
+    val rdd1 = sparkContext.parallelize((0 to 1).map(i => nullCheckData1(i)))
+    rdd1.registerTempTable("nulldata1")
+    val nullCheckData2 = TestData(1,"1") :: TestData(2,null) :: Nil
+    val rdd2 = sparkContext.parallelize((0 to 1).map(i => nullCheckData2(i)))
+    rdd2.registerTempTable("nulldata2")
+    checkAnswer(sql("SELECT nulldata1.key FROM nulldata1 join " +
+      "nulldata2 on nulldata1.value <=> nulldata2.value"),
+        (1 to 2).map(i => Seq(i)))
+  }
 }