address lian cheng's comments

Author: adrian-wang

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

@@ -62,6 +62,7 @@ case class Cast(child: Expression, dataType: DataType) extends UnaryExpression w
     case TimestampType =>
       buildCast[Timestamp](_, t => t.getTime() != 0 || t.getNanos() != 0)
     case DateType =>
+      // Hive would return null when cast from date to boolean
       buildCast[Date](_, d => null)
     case LongType =>
       buildCast[Long](_, _ != 0)

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/types/dataTypes.scala

@@ -256,7 +256,7 @@ case object DateType extends NativeType {
   @transient private[sql] lazy val tag = ScalaReflectionLock.synchronized { typeTag[JvmType] }
 
   private[sql] val ordering = new Ordering[JvmType] {
-    def compare(x: Date, y: Date) = x.toString.compareTo(y.toString)
+    def compare(x: Date, y: Date) = x.compareTo(y)
   }
 }
 

sql/core/src/main/scala/org/apache/spark/sql/columnar/ColumnStats.scala

@@ -198,8 +198,8 @@ private[sql] class DateColumnStats extends ColumnStats {
   override def gatherStats(row: Row, ordinal: Int) {
     if (!row.isNullAt(ordinal)) {
       val value = row(ordinal).asInstanceOf[Date]
-      if (upper == null || value.toString.compareTo(upper.toString) > 0) upper = value
-      if (lower == null || value.toString.compareTo(lower.toString) < 0) lower = value
+      if (upper == null || value.compareTo(upper) > 0) upper = value
+      if (lower == null || value.compareTo(lower) < 0) lower = value
     } else {
       nullCount += 1
     }

sql/core/src/main/scala/org/apache/spark/sql/columnar/ColumnType.scala

@@ -341,15 +341,15 @@ private[sql] object DATE extends NativeColumnType(DateType, 8, 8) {
     date
   }
 
-  override def append(v: Date, buffer: ByteBuffer) {
+  override def append(v: Date, buffer: ByteBuffer): Unit = {
     buffer.putLong(v.getTime)
   }
 
   override def getField(row: Row, ordinal: Int) = {
     row(ordinal).asInstanceOf[Date]
   }
 
-  override def setField(row: MutableRow, ordinal: Int, value: Date) {
+  override def setField(row: MutableRow, ordinal: Int, value: Date): Unit = {
     row(ordinal) = value
   }
 }