Github user liancheng commented on a diff in the pull request:
https://github.com/apache/spark/pull/14897#discussion_r80281859
--- Diff:
sql/core/src/main/scala/org/apache/spark/sql/execution/command/views.scala ---
@@ -19,13 +19,46 @@ package org.apache.spark.sql.execution.command
import scala.util.control.NonFatal
-import org.apache.spark.sql.{AnalysisException, Row, SparkSession}
+import org.apache.spark.sql.{AnalysisException, Dataset, Row, SparkSession}
import org.apache.spark.sql.catalyst.{SQLBuilder, TableIdentifier}
import org.apache.spark.sql.catalyst.catalog.{CatalogStorageFormat,
CatalogTable, CatalogTableType}
import org.apache.spark.sql.catalyst.expressions.Alias
import org.apache.spark.sql.catalyst.plans.QueryPlan
import org.apache.spark.sql.catalyst.plans.logical.{LogicalPlan, Project}
-import org.apache.spark.sql.types.StructType
+import org.apache.spark.sql.execution.datasources.{DataSource,
LogicalRelation}
+import org.apache.spark.sql.types.{MetadataBuilder, StructType}
+
+
+/**
+ * ViewType is used to specify the expected view type when we want to
create or replace a view in
+ * [[CreateViewCommand]].
+ */
+sealed trait ViewType
+
+/**
+ * LocalTempView means session-scoped local temporary views. Its lifetime
is the lifetime of the
+ * session that created it, i.e. it will be automatically dropped when the
session terminates. It's
+ * not tied to any databases, i.e. we can't use `db1.view1` to reference a
local temporary view.
+ */
+object LocalTempView extends ViewType
+
+/**
+ * GlobalTempView means cross-session global temporary views. Its lifetime
is the lifetime of the
+ * Spark application, i.e. it will be automatically dropped when the
application terminates. It's
+ * tied to a system preserved database `_global_temp`, and we must use the
qualified name to refer a
+ * global temp view, e.g. SELECT * FROM _global_temp.view1.
+ */
+object GlobalTempView extends ViewType
+
+/**
+ * PermanentView means cross-session permanent views. Permanent views stay
until they are
+ * explicitly dropped by user command. It's always tied to a database,
default to the current
+ * database if not specified.
+ *
+ * Note that, Existing permanent view with the same name are not visible
to the current session
+ * while the local temporary view exists, unless the view name is
qualified by database.
+ */
+object PermanentView extends ViewType
--- End diff --
Is `PersistedView` a more conventional name?
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