Github user jiangxb1987 commented on a diff in the pull request:
https://github.com/apache/spark/pull/16233#discussion_r95510361
--- Diff:
sql/hive/src/main/scala/org/apache/spark/sql/hive/HiveMetastoreCatalog.scala ---
@@ -125,11 +132,16 @@ private[hive] class
HiveMetastoreCatalog(sparkSession: SparkSession) extends Log
// Otherwise, wrap the table with a Subquery using the table name.
alias.map(a => SubqueryAlias(a, qualifiedTable,
None)).getOrElse(qualifiedTable)
} else if (table.tableType == CatalogTableType.VIEW) {
+ val tableIdentifier = table.identifier
val viewText = table.viewText.getOrElse(sys.error("Invalid view
without text."))
- SubqueryAlias(
- alias.getOrElse(table.identifier.table),
- sparkSession.sessionState.sqlParser.parsePlan(viewText),
- Option(table.identifier))
+ // The relation is a view, so we wrap the relation by:
+ // 1. Add a [[View]] operator over the relation to keep track of the
view desc;
+ // 2. Wrap the logical plan in a [[SubqueryAlias]] which tracks the
name of the view.
+ val child = View(
+ desc = table,
+ output = table.schema.toAttributes,
+ child = sparkSession.sessionState.sqlParser.parsePlan(viewText))
--- End diff --
The resolution of a View operator takes place by two stages:
For the first stage, we look up the relation and generate a View node by:
1. Parse the `viewText` to generate a child logical plan, which is
unresolved;
2. Generate the output attribute from the `CatalogTable.schema`, which is
resolved;
This stage focus on planning of the view.
For the second stage, we resolve the child logical plan of the View node,
the logic is in `ResolveRelations.resolveRelation()`.
In this stage, we resolve the child logical plan, which was parsed from the
`viewText`(the sql query string that creates the view).
At last, in `AliasViewChild` rule, we alias the resolved child plan to the
view node. In this way, we successfully resolve a view.
In the future, we could cache the `viewText` and its corresponding logical
plan. In case a view is referenced for multiple times, we only have to parse
and resolve the query for once, and for later references we can read directly
from the cache.
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