fix py

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/unresolved.scala

@@ -546,17 +546,27 @@ case class UnresolvedOrdinal(ordinal: Int)
 }
 
 trait UnresolvedBinaryExpression extends BinaryExpression with Unevaluable {
+  val operator: String
   override lazy val resolved: Boolean = false
   override def dataType: DataType = throw new UnresolvedException(this, "dataType")
+  override def sql: String = s"${left.sql} $operator ${right.sql}"
 }
 
-case class UnresolvedAdd(left: Expression, right: Expression) extends UnresolvedBinaryExpression
+case class UnresolvedAdd(left: Expression, right: Expression) extends UnresolvedBinaryExpression {
+  override val operator: String = "+"
+}
 
 case class UnresolvedSubtract(left: Expression, right: Expression)
-  extends UnresolvedBinaryExpression
+  extends UnresolvedBinaryExpression {
+  override val operator: String = "-"
+}
 
 case class UnresolvedMultiply(left: Expression, right: Expression)
-  extends UnresolvedBinaryExpression
+  extends UnresolvedBinaryExpression {
+  override val operator: String = "*"
+}
 
 case class UnresolvedDivide(left: Expression, right: Expression)
-  extends UnresolvedBinaryExpression
+  extends UnresolvedBinaryExpression {
+  override val operator: String = "/"
+}