name : group_by_handler.h /* 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; /* Number of auxiliary fields. */ int n_aux; 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, except for const items and some other exceptions, see Create_tmp_table::add_fields() for which items are included and which are skipped. */ TABLE *table; group_by_handler(THD *thd_arg, handlerton *ht_arg) : thd(thd_arg), ht(ht_arg), table(0) {} virtual ~group_by_handler() = default; /* 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