Keep the current behavior and add new error message for dropping current db.

Author: dongjoon-hyun

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

@@ -148,8 +148,10 @@ class SessionCatalog(
 
   def dropDatabase(db: String, ignoreIfNotExists: Boolean, cascade: Boolean): Unit = {
     val dbName = formatDatabaseName(db)
-    if (dbName == DEFAULT_DATABASE || dbName == getCurrentDatabase) {
-      throw new AnalysisException(s"Can not drop `${DEFAULT_DATABASE}` or current database")
+    if (dbName == DEFAULT_DATABASE) {
+      throw new AnalysisException(s"Can not drop default database")
+    } else if (dbName == getCurrentDatabase) {
+      throw new AnalysisException(s"Can not drop current database `${dbName}`")
     }
     externalCatalog.dropDatabase(dbName, ignoreIfNotExists, cascade)
   }

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

@@ -1270,28 +1270,30 @@ class DDLSuite extends QueryTest with SharedSQLContext with BeforeAndAfterEach {
       "WITH SERDEPROPERTIES ('spark.sql.sources.me'='anything')")
   }
 
-  test("drop default or current database") {
+  test("drop current database") {
     sql("CREATE DATABASE temp")
     sql("USE temp")
     val m = intercept[AnalysisException] {
       sql("DROP DATABASE temp")
     }.getMessage
-    assert(m.contains("Can not drop `default` or current database"))
+    assert(m.contains("Can not drop current database `temp`"))
+  }
 
+  test("drop default database") {
     Seq("true", "false").foreach { caseSensitive =>
       withSQLConf(SQLConf.CASE_SENSITIVE.key -> caseSensitive) {
         var message = intercept[AnalysisException] {
           sql("DROP DATABASE default")
         }.getMessage
-        assert(message.contains("Can not drop `default` or current database"))
+        assert(message.contains("Can not drop default database"))
 
         message = intercept[AnalysisException] {
           sql("DROP DATABASE DeFault")
         }.getMessage
         if (caseSensitive == "true") {
           assert(message.contains("Database 'DeFault' not found"))
         } else {
-          assert(message.contains("Can not drop `default` or current database"))
+          assert(message.contains("Can not drop default database"))
         }
       }
     }

sql/hive/src/test/scala/org/apache/spark/sql/hive/execution/HiveDDLSuite.scala

@@ -567,18 +567,14 @@ class HiveDDLSuite
         var message = intercept[AnalysisException] {
           sql("DROP DATABASE default")
         }.getMessage
-        assert(message.contains("Can not drop `default` or current database"))
+        assert(message.contains("Can not drop default database"))
 
         // SQLConf.CASE_SENSITIVE does not affect the result
         // because the Hive metastore is not case sensitive.
         message = intercept[AnalysisException] {
           sql("DROP DATABASE DeFault")
         }.getMessage
-        if (caseSensitive == "true") {
-          assert(message.contains("Can not drop default database"))
-        } else {
-          assert(message.contains("Can not drop `default` or current database"))
-        }
+        assert(message.contains("Can not drop default database"))
       }
     }
   }