[SPARK-9495] prefix of DateType/TimestampType

cc rxin

Author: Davies Liu <davies@databricks.com>

Closes #7856 from davies/sort_improve and squashes the following commits:

5fc81bd [Davies Liu] support DateType/TimestampType

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

@@ -61,6 +61,8 @@ case class SortPrefix(child: SortOrder) extends UnaryExpression {
         (Long.MinValue, s"$input ? 1L : 0L")
       case _: IntegralType =>
         (Long.MinValue, s"(long) $input")
+      case DateType | TimestampType =>
+        (Long.MinValue, s"(long) $input")
       case FloatType | DoubleType =>
         (DoublePrefixComparator.computePrefix(Double.NegativeInfinity),
           s"$DoublePrefixCmp.computePrefix((double)$input)")

sql/core/src/main/scala/org/apache/spark/sql/execution/SortPrefixUtils.scala

@@ -38,9 +38,11 @@ object SortPrefixUtils {
     sortOrder.dataType match {
       case StringType if sortOrder.isAscending => PrefixComparators.STRING
       case StringType if !sortOrder.isAscending => PrefixComparators.STRING_DESC
-      case BooleanType | ByteType | ShortType | IntegerType | LongType if sortOrder.isAscending =>
+      case BooleanType | ByteType | ShortType | IntegerType | LongType | DateType | TimestampType
+          if sortOrder.isAscending =>
         PrefixComparators.LONG
-      case BooleanType | ByteType | ShortType | IntegerType | LongType if !sortOrder.isAscending =>
+      case BooleanType | ByteType | ShortType | IntegerType | LongType | DateType | TimestampType
+        if !sortOrder.isAscending =>
         PrefixComparators.LONG_DESC
       case FloatType | DoubleType if sortOrder.isAscending => PrefixComparators.DOUBLE
       case FloatType | DoubleType if !sortOrder.isAscending => PrefixComparators.DOUBLE_DESC