MDEV-10846 Running mysqldump backup twice returns error: Table

           'mysql.proc' doesn't exist.

        The mysql_rm_db() doesn't seem to expect the 'mysql' database
        to be deleted. Checks for that added.
        Also fixed the bug MDEV-11105 Table named 'db'
        has weird side effect.
        The db.opt file now removed separately.

Author: Alexey Botchkov

mysql-test/r/drop.result

@@ -209,3 +209,9 @@ INSERT INTO table1 VALUES (1);
 ERROR 42S02: Unknown table 't.notable'
 DROP TABLE table1,table2;
 # End BUG#34750
+#
+# MDEV-11105 Table named 'db' has weird side effect.
+#
+CREATE DATABASE mysqltest;
+CREATE TABLE mysqltest.db(id INT);
+DROP DATABASE mysqltest;

mysql-test/t/drop.test

@@ -313,3 +313,12 @@ INSERT INTO table1 VALUES (1);
 DROP TABLE table1,table2;
 
 --echo # End BUG#34750
+
+--echo #
+--echo # MDEV-11105 Table named 'db' has weird side effect.
+--echo #
+
+CREATE DATABASE mysqltest;
+CREATE TABLE mysqltest.db(id INT);
+DROP DATABASE mysqltest;
+

sql/sql_db.cc

@@ -784,7 +784,7 @@ bool mysql_alter_db(THD *thd, const char *db, HA_CREATE_INFO *create_info)
 bool mysql_rm_db(THD *thd,char *db,bool if_exists, bool silent)
 {
   ulong deleted_tables= 0;
-  bool error= true;
+  bool error= true, rm_mysql_schema;
   char	path[FN_REFLEN + 16];
   MY_DIR *dirp;
   uint length;
@@ -809,6 +809,18 @@ bool mysql_rm_db(THD *thd,char *db,bool if_exists, bool silent)
   length= build_table_filename(path, sizeof(path) - 1, db, "", "", 0);
   strmov(path+length, MY_DB_OPT_FILE);		// Append db option file name
   del_dbopt(path);				// Remove dboption hash entry
+  /*
+     Now remove the db.opt file.
+     The 'find_db_tables_and_rm_known_files' doesn't remove this file
+     if there exists a table with the name 'db', so let's just do it
+     separately. We know this file exists and needs to be deleted anyway.
+  */
+  if (my_delete_with_symlink(path, MYF(0)) && my_errno != ENOENT)
+  {
+    my_error(EE_DELETE, MYF(0), path, my_errno);
+    DBUG_RETURN(true);
+  }
+    
   path[length]= '\0';				// Remove file name
 
   /* See if the directory exists */
@@ -835,7 +847,8 @@ bool mysql_rm_db(THD *thd,char *db,bool if_exists, bool silent)
     Disable drop of enabled log tables, must be done before name locking.
     This check is only needed if we are dropping the "mysql" database.
   */
-  if ((my_strcasecmp(system_charset_info, MYSQL_SCHEMA_NAME.str, db) == 0))
+  if ((rm_mysql_schema=
+        (my_strcasecmp(system_charset_info, MYSQL_SCHEMA_NAME.str, db) == 0)))
   {
     for (table= tables; table; table= table->next_local)
       if (check_if_log_table(table, TRUE, "DROP"))
@@ -848,7 +861,7 @@ bool mysql_rm_db(THD *thd,char *db,bool if_exists, bool silent)
       lock_db_routines(thd, dbnorm))
     goto exit;
 
-  if (!in_bootstrap)
+  if (!in_bootstrap && !rm_mysql_schema)
   {
     for (table= tables; table; table= table->next_local)
     {
@@ -893,10 +906,13 @@ bool mysql_rm_db(THD *thd,char *db,bool if_exists, bool silent)
     ha_drop_database(path);
     tmp_disable_binlog(thd);
     query_cache_invalidate1(thd, dbnorm);
-    (void) sp_drop_db_routines(thd, dbnorm); /* @todo Do not ignore errors */
+    if (!rm_mysql_schema)
+    {
+      (void) sp_drop_db_routines(thd, dbnorm); /* @todo Do not ignore errors */
 #ifdef HAVE_EVENT_SCHEDULER
-    Events::drop_schema_events(thd, dbnorm);
+      Events::drop_schema_events(thd, dbnorm);
 #endif
+    }
     reenable_binlog(thd);
 
     /*