[SPARK-4755] [SQL] sqrt(negative value) should return null

Author: Daoyuan Wang <daoyuan.wang@intel.com>

Closes #3616 from adrian-wang/sqrt and squashes the following commits:

d877439 [Daoyuan Wang] fix NULLTYPE
3effa2c [Daoyuan Wang] sqrt(negative value) should return null

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/arithmetic.scala

@@ -38,11 +38,22 @@ case class Sqrt(child: Expression) extends UnaryExpression {
 
   def dataType = DoubleType
   override def foldable = child.foldable
-  def nullable = child.nullable
+  def nullable = true
   override def toString = s"SQRT($child)"
 
   override def eval(input: Row): Any = {
-    n1(child, input, (na,a) => math.sqrt(na.toDouble(a)))
+    val evalE = child.eval(input)
+    if (evalE == null) {
+      null
+    } else {
+      child.dataType match {
+        case n: NumericType =>
+          val value = n.numeric.toDouble(evalE.asInstanceOf[n.JvmType])
+          if (value < 0) null
+          else math.sqrt(value)
+        case other => sys.error(s"Type $other does not support non-negative numeric operations")
+      }
+    }
   }
 }
 

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/expressions/ExpressionEvaluationSuite.scala

@@ -1037,6 +1037,8 @@ class ExpressionEvaluationSuite extends FunSuite {
     }
 
     checkEvaluation(Sqrt(Literal(null, DoubleType)), null, new GenericRow(Array[Any](null)))
+    checkEvaluation(Sqrt(-1), null, EmptyRow)
+    checkEvaluation(Sqrt(-1.5), null, EmptyRow)
   }
 
   test("Bitwise operations") {