MDEV-17096 Pushdown of simple derived tables to storage engines

MDEV-17631 select_handler for a full query pushdown

Added comments and file headers for files introduced in these tasks.

1 files changed, 53 insertions, 10 deletions

diff --git a/sql/derived_handler.cc b/sql/derived_handler.cc
index 1fa5e94a1d4..76fd736de2b 100644
--- a/sql/derived_handler.cc
+++ b/sql/derived_handler.cc
@@ -1,18 +1,41 @@
+/*
+   Copyright (c) 2018, 2019 MariaDB
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; version 2 of the License.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program; if not, write to the Free Software
+   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02111-1301 USA */
+
 #include "mariadb.h"
 #include "sql_priv.h"
 #include "sql_select.h"
 #include "derived_handler.h"
 
-void derived_handler::set_derived(TABLE_LIST *tbl)
-{
-  derived= tbl;
-  table= tbl->table;
-  unit= tbl->derived;
-  select= unit->first_select();
-  tmp_table_param= select->next_select() ?
-                   ((select_unit *)(unit->result))->get_tmp_table_param() :
-                   &select->join->tmp_table_param;
-}
+
+/**
+  The methods of the Pushdown_derived class.
+
+  The objects of this class are used for pushdown of the derived tables
+  into engines. The main  method of the class is Pushdown_derived::execute()
+  that initiates execution of the query specifying a derived by a foreign
+  engine, receives the rows of the result set and put them in a temporary
+  table on the server side.
+
+  The method uses only the functions of the derived_handle interface to do
+  this. The constructor of the class gets this interface as a parameter.
+
+  Currently a derived tables pushed into an engine is always materialized.
+  It could be changed if the cases when the tables is used as driving table.
+*/
+
 
 Pushdown_derived::Pushdown_derived(TABLE_LIST *tbl, derived_handler *h)
  : derived(tbl), handler(h)
@@ -20,11 +43,13 @@ Pushdown_derived::Pushdown_derived(TABLE_LIST *tbl, derived_handler *h)
   is_analyze= handler->thd->lex->analyze_stmt;
 }
 
+
 Pushdown_derived::~Pushdown_derived()
 {
   delete handler;
 }
 
+
 int Pushdown_derived::execute()
 {
   int err;
@@ -82,3 +107,21 @@ error_2:
   DBUG_RETURN(-1);                              // Error not sent to client
 }
 
+
+void derived_handler::print_error(int error, myf errflag)
+{
+  my_error(ER_GET_ERRNO, MYF(0), error, hton_name(ht)->str);
+}
+
+
+void derived_handler::set_derived(TABLE_LIST *tbl)
+{
+  derived= tbl;
+  table= tbl->table;
+  unit= tbl->derived;
+  select= unit->first_select();
+  tmp_table_param= select->next_select() ?
+                   ((select_unit *)(unit->result))->get_tmp_table_param() :
+                   &select->join->tmp_table_param;
+}
+