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diff --git a/sql/group_by_handler.h b/sql/group_by_handler.h
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+/*
+   Copyright (c) 2014, 2015 SkySQL Ab & MariaDB Foundation
+
+   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 02110-1335 USA */
+
+#ifndef GROUP_BY_HANDLER_INCLUDED
+#define GROUP_BY_HANDLER_INCLUDED
+
+class Select_limit_counters;
+/*
+  This file implements the group_by_handler interface. This interface
+  can be used by storage handlers that can intercept summary or GROUP
+  BY queries from MariaDB and itself return the result to the user or
+  upper level. It is part of the Storage Engine API
+
+  Both main and sub queries are supported. Here are some examples of what the
+  storage engine could intersept:
+
+  SELECT count(*) FROM t1;
+  SELECT a,count(*) FROM t1 group by a;
+  SELECT a,count(*) as sum FROM t1 where b > 10 group by a, order by sum;
+  SELECT a,count(*) FROM t1,t2;
+  SELECT a, (select sum(*) from t2 where t1.a=t2.a) from t2;
+*/
+
+/**
+  The structure describing various parts of the query
+
+  The engine is supposed to take out parts that it can do internally.
+  For example, if the engine can return results sorted according to
+  the specified order_by clause, it sets Query::order_by=NULL before
+  returning.
+
+  At the moment the engine must take group_by (or return an error), and
+  optionally can take distinct, where, order_by, and having.
+
+  The engine should not modify the select list. It is the extended SELECT
+  clause (extended, because it has more items than the original
+  user-specified SELECT clause) and it contains all aggregate functions,
+  used in the query.
+*/
+struct Query
+{
+  List<Item> *select;
+  bool        distinct;
+  TABLE_LIST *from;
+  Item       *where;
+  ORDER      *group_by;
+  ORDER      *order_by;
+  Item       *having;
+  // LIMIT
+  Select_limit_counters *limit;
+};
+
+class group_by_handler
+{
+public:
+  THD *thd;
+  handlerton *ht;
+
+  /*
+    Temporary table where all results should be stored in record[0]
+    The table has a field for every item from the Query::select list.
+  */
+  TABLE *table;
+
+  group_by_handler(THD *thd_arg, handlerton *ht_arg)
+    : thd(thd_arg), ht(ht_arg), table(0) {}
+  virtual ~group_by_handler() {}
+
+  /*
+    Functions to scan data. All these returns 0 if ok, error code in case
+    of error
+  */
+
+  /*
+    Initialize group_by scan, prepare for next_row().
+    If this is a sub query with group by, this can be called many times for
+    a query.
+  */
+  virtual int init_scan()= 0;
+
+  /*
+    Return next group by result in table->record[0].
+    Return 0 if row found, HA_ERR_END_OF_FILE if last row and other error
+    number in case of fatal error.
+   */
+  virtual int next_row()= 0;
+
+  /* End scanning */
+  virtual int end_scan()=0;
+
+  /* Report errors */
+  virtual void print_error(int error, myf errflag);
+};
+
+#endif //GROUP_BY_HANDLER_INCLUDED