[SPARK-16374][SQL] Remove Alias from MetastoreRelation and SimpleCatalogRelation

#### What changes were proposed in this pull request?
Different from the other leaf nodes, `MetastoreRelation` and `SimpleCatalogRelation` have a pre-defined `alias`, which is used to change the qualifier of the node. However, based on the existing alias handling, alias should be put in `SubqueryAlias`.

This PR is to separate alias handling from `MetastoreRelation` and `SimpleCatalogRelation` to make it consistent with the other nodes. It simplifies the signature and conversion to a `BaseRelation`.

For example, below is an example query for `MetastoreRelation`,  which is converted to a `LogicalRelation`:
```SQL
SELECT tmp.a + 1 FROM test_parquet_ctas tmp WHERE tmp.a > 2
```

Before changes, the analyzed plan is
```
== Analyzed Logical Plan ==
(a + 1): int
Project [(a#951 + 1) AS (a + 1)#952]
+- Filter (a#951 > 2)
   +- SubqueryAlias tmp
      +- Relation[a#951] parquet
```
After changes, the analyzed plan becomes
```
== Analyzed Logical Plan ==
(a + 1): int
Project [(a#951 + 1) AS (a + 1)#952]
+- Filter (a#951 > 2)
   +- SubqueryAlias tmp
      +- SubqueryAlias test_parquet_ctas
         +- Relation[a#951] parquet
```

**Note: the optimized plans are the same.**

For `SimpleCatalogRelation`, the existing code always generates two Subqueries. Thus, no change is needed.

#### How was this patch tested?
Added test cases.

Author: gatorsmile <gatorsmile@gmail.com>

Closes #14053 from gatorsmile/removeAliasFromMetastoreRelation.

2 files changed, 10 insertions, 10 deletions

diff --git a/sql/hive/src/main/scala/org/apache/spark/sql/hive/HiveMetastoreCatalog.scala b/sql/hive/src/main/scala/org/apache/spark/sql/hive/HiveMetastoreCatalog.scala
index 20e64a4e09..2be51ed0e8 100644
--- a/sql/hive/src/main/scala/org/apache/spark/sql/hive/HiveMetastoreCatalog.scala
+++ b/sql/hive/src/main/scala/org/apache/spark/sql/hive/HiveMetastoreCatalog.scala
@@ -180,8 +180,10 @@ private[hive] class HiveMetastoreCatalog(sparkSession: SparkSession) extends Log
           SubqueryAlias(aliasText, sessionState.sqlParser.parsePlan(viewText))
       }
     } else {
-      MetastoreRelation(
-        qualifiedTableName.database, qualifiedTableName.name, alias)(table, client, sparkSession)
+      val qualifiedTable =
+        MetastoreRelation(
+          qualifiedTableName.database, qualifiedTableName.name)(table, client, sparkSession)
+      alias.map(a => SubqueryAlias(a, qualifiedTable)).getOrElse(qualifiedTable)
     }
   }
 
@@ -385,7 +387,7 @@ private[hive] class HiveMetastoreCatalog(sparkSession: SparkSession) extends Log
         // Read path
         case relation: MetastoreRelation if shouldConvertMetastoreParquet(relation) =>
           val parquetRelation = convertToParquetRelation(relation)
-          SubqueryAlias(relation.alias.getOrElse(relation.tableName), parquetRelation)
+          SubqueryAlias(relation.tableName, parquetRelation)
       }
     }
   }
@@ -423,7 +425,7 @@ private[hive] class HiveMetastoreCatalog(sparkSession: SparkSession) extends Log
         // Read path
         case relation: MetastoreRelation if shouldConvertMetastoreOrc(relation) =>
           val orcRelation = convertToOrcRelation(relation)
-          SubqueryAlias(relation.alias.getOrElse(relation.tableName), orcRelation)
+          SubqueryAlias(relation.tableName, orcRelation)
       }
     }
   }
diff --git a/sql/hive/src/main/scala/org/apache/spark/sql/hive/MetastoreRelation.scala b/sql/hive/src/main/scala/org/apache/spark/sql/hive/MetastoreRelation.scala
index 58bca2059c..3ab1bdabb9 100644
--- a/sql/hive/src/main/scala/org/apache/spark/sql/hive/MetastoreRelation.scala
+++ b/sql/hive/src/main/scala/org/apache/spark/sql/hive/MetastoreRelation.scala
@@ -41,8 +41,7 @@ import org.apache.spark.sql.hive.client.HiveClient
 
 private[hive] case class MetastoreRelation(
     databaseName: String,
-    tableName: String,
-    alias: Option[String])
+    tableName: String)
     (val catalogTable: CatalogTable,
      @transient private val client: HiveClient,
      @transient private val sparkSession: SparkSession)
@@ -52,13 +51,12 @@ private[hive] case class MetastoreRelation(
     case relation: MetastoreRelation =>
       databaseName == relation.databaseName &&
         tableName == relation.tableName &&
-        alias == relation.alias &&
         output == relation.output
     case _ => false
   }
 
   override def hashCode(): Int = {
-    Objects.hashCode(databaseName, tableName, alias, output)
+    Objects.hashCode(databaseName, tableName, output)
   }
 
   override protected def otherCopyArgs: Seq[AnyRef] = catalogTable :: sparkSession :: Nil
@@ -208,7 +206,7 @@ private[hive] case class MetastoreRelation(
       CatalystSqlParser.parseDataType(f.dataType),
       // Since data can be dumped in randomly with no validation, everything is nullable.
       nullable = true
-    )(qualifier = Some(alias.getOrElse(tableName)))
+    )(qualifier = Some(tableName))
   }
 
   /** PartitionKey attributes */
@@ -243,6 +241,6 @@ private[hive] case class MetastoreRelation(
   }
 
   override def newInstance(): MetastoreRelation = {
-    MetastoreRelation(databaseName, tableName, alias)(catalogTable, client, sparkSession)
+    MetastoreRelation(databaseName, tableName)(catalogTable, client, sparkSession)
   }
 }