Github user yhuai commented on a diff in the pull request:
https://github.com/apache/spark/pull/16233#discussion_r93898653
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/catalog/SessionCatalog.scala
---
@@ -551,17 +551,26 @@ class SessionCatalog(
*
* If a database is specified in `name`, this will return the table/view
from that database.
* If no database is specified, this will first attempt to return a
temporary table/view with
- * the same name, then, if that does not exist, return the table/view
from the current database.
+ * the same name, then, if that does not exist, and defaultDatabase is
defined, return the
+ * table/view from the defaultDatabase, else return the table/view from
the catalog.currentDb.
*
* Note that, the global temp view database is also valid here, this
will return the global temp
* view matching the given name.
*
- * If the relation is a view, the relation will be wrapped in a
[[SubqueryAlias]] which will
- * track the name of the view.
+ * If the relation is a view, we generate a [[View]] operator from the
view description, and
+ * wrap the logical plan in a [[SubqueryAlias]] which will track the
name of the view.
+ *
+ * @param name The name of the table/view that we lookup.
+ * @param alias The alias name of the table/view that we lookup.
+ * @param defaultDatabase The database name we should use to lookup the
table/view, if the
+ * database part of [[TableIdentifier]] is not
defined.
--- End diff --
Let's also explain the precedence (db name in the table identifier ->
default db -> current db).
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