[SPARK-15184][SQL] Fix Silent Removal of An Existent Temp Table by Rename Table

#### What changes were proposed in this pull request?
Currently, if we rename a temp table `Tab1` to another existent temp table `Tab2`. `Tab2` will be silently removed. This PR is to detect it and issue an exception message.

In addition, this PR also detects another issue in the rename table command. When the destination table identifier does have database name, we should not ignore them. That might mean users could rename a regular table.

#### How was this patch tested?
Added two related test cases

Author: gatorsmile <gatorsmile@gmail.com>

Closes #12959 from gatorsmile/rewriteTable.

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

@@ -301,6 +301,15 @@ class SessionCatalog(
     if (oldName.database.isDefined || !tempTables.contains(oldTableName)) {
       externalCatalog.renameTable(db, oldTableName, newTableName)
     } else {
+      if (newName.database.isDefined) {
+        throw new AnalysisException(
+          s"RENAME TEMPORARY TABLE from '$oldName' to '$newName': cannot specify database " +
+            s"name '${newName.database.get}' in the destination table")
+      }
+      if (tempTables.contains(newTableName)) {
+        throw new AnalysisException(
+          s"RENAME TEMPORARY TABLE from '$oldName' to '$newName': destination table already exists")
+      }
       val table = tempTables(oldTableName)
       tempTables.remove(oldTableName)
       tempTables.put(newTableName, table)

sql/core/src/test/scala/org/apache/spark/sql/execution/command/DDLSuite.scala

@@ -396,6 +396,66 @@ class DDLSuite extends QueryTest with SharedSQLContext with BeforeAndAfterEach {
     }
   }
 
+  test("rename temporary table - destination table with database name") {
+    withTempTable("tab1") {
+      sql(
+        """
+          |CREATE TEMPORARY TABLE tab1
+          |USING org.apache.spark.sql.sources.DDLScanSource
+          |OPTIONS (
+          |  From '1',
+          |  To '10',
+          |  Table 'test1'
+          |)
+        """.stripMargin)
+
+      val e = intercept[AnalysisException] {
+        sql("ALTER TABLE tab1 RENAME TO default.tab2")
+      }
+      assert(e.getMessage.contains(
+        "RENAME TEMPORARY TABLE from '`tab1`' to '`default`.`tab2`': " +
+          "cannot specify database name 'default' in the destination table"))
+
+      val catalog = sqlContext.sessionState.catalog
+      assert(catalog.listTables("default") == Seq(TableIdentifier("tab1")))
+    }
+  }
+
+  test("rename temporary table - destination table already exists") {
+    withTempTable("tab1", "tab2") {
+      sql(
+        """
+          |CREATE TEMPORARY TABLE tab1
+          |USING org.apache.spark.sql.sources.DDLScanSource
+          |OPTIONS (
+          |  From '1',
+          |  To '10',
+          |  Table 'test1'
+          |)
+        """.stripMargin)
+
+      sql(
+        """
+          |CREATE TEMPORARY TABLE tab2
+          |USING org.apache.spark.sql.sources.DDLScanSource
+          |OPTIONS (
+          |  From '1',
+          |  To '10',
+          |  Table 'test1'
+          |)
+        """.stripMargin)
+
+      val e = intercept[AnalysisException] {
+        sql("ALTER TABLE tab1 RENAME TO tab2")
+      }
+      assert(e.getMessage.contains(
+        "RENAME TEMPORARY TABLE from '`tab1`' to '`tab2`': destination table already exists"))
+
+      val catalog = sqlContext.sessionState.catalog
+      assert(catalog.listTables("default") == Seq(TableIdentifier("tab1"), TableIdentifier("tab2")))
+    }
+  }
+
   test("alter table: set location") {
     testSetLocation(isDatasourceTable = false)
   }