improve the disply of CatalogTable information

Author: bomeng

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/catalog/interface.scala

@@ -127,7 +127,7 @@ case class CatalogTable(
     sortColumnNames: Seq[String] = Seq.empty,
     bucketColumnNames: Seq[String] = Seq.empty,
     numBuckets: Int = -1,
-    owner: String = "",
+    owner: String = System.getProperty("user.name"),
     createTime: Long = System.currentTimeMillis,
     lastAccessTime: Long = -1,
     properties: Map[String, String] = Map.empty,
@@ -180,7 +180,8 @@ case class CatalogTable(
       Seq(s"Table: ${identifier.quotedString}",
         if (owner.nonEmpty) s"Owner: $owner" else "",
         s"Created: ${new Date(createTime).toString}",
-        s"Last Access: ${new Date(lastAccessTime).toString}",
+        "Last Access: " +
+          (if (lastAccessTime == -1) "UNKNOWN" else new Date(lastAccessTime).toString),
         s"Type: ${tableType.name}",
         if (schema.nonEmpty) s"Schema: ${schema.mkString("[", ", ", "]")}" else "",
         if (partitionColumnNames.nonEmpty) s"Partition Columns: $partitionColumns" else "",

sql/core/src/main/scala/org/apache/spark/sql/execution/command/tables.scala

@@ -468,7 +468,8 @@ case class DescribeTableCommand(table: TableIdentifier, isExtended: Boolean, isF
     append(buffer, "Database:", table.database, "")
     append(buffer, "Owner:", table.owner, "")
     append(buffer, "Create Time:", new Date(table.createTime).toString, "")
-    append(buffer, "Last Access Time:", new Date(table.lastAccessTime).toString, "")
+    append(buffer, "Last Access Time:",
+      if (table.lastAccessTime == -1) "UNKNOWN" else new Date(table.lastAccessTime).toString, "")
     append(buffer, "Location:", table.storage.locationUri.getOrElse(""), "")
     append(buffer, "Table Type:", table.tableType.name, "")
 
@@ -522,7 +523,7 @@ case class DescribeTableCommand(table: TableIdentifier, isExtended: Boolean, isF
 
   private def describeSchema(schema: Seq[CatalogColumn], buffer: ArrayBuffer[Row]): Unit = {
     schema.foreach { column =>
-      append(buffer, column.name, column.dataType.toLowerCase, column.comment.orNull)
+      append(buffer, column.name, column.dataType.toLowerCase, column.comment.getOrElse(""))
     }
   }