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108 lines
3.2 KiB
C++
108 lines
3.2 KiB
C++
/*
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Copyright (c) 2014, 2015 SkySQL Ab & MariaDB Foundation
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; version 2 of the License.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program; if not, write to the Free Software
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Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1335 USA */
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#ifndef GROUP_BY_HANDLER_INCLUDED
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#define GROUP_BY_HANDLER_INCLUDED
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class Select_limit_counters;
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/*
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This file implements the group_by_handler interface. This interface
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can be used by storage handlers that can intercept summary or GROUP
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BY queries from MariaDB and itself return the result to the user or
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upper level. It is part of the Storage Engine API
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Both main and sub queries are supported. Here are some examples of what the
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storage engine could intersept:
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SELECT count(*) FROM t1;
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SELECT a,count(*) FROM t1 group by a;
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SELECT a,count(*) as sum FROM t1 where b > 10 group by a, order by sum;
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SELECT a,count(*) FROM t1,t2;
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SELECT a, (select sum(*) from t2 where t1.a=t2.a) from t2;
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*/
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/**
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The structure describing various parts of the query
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The engine is supposed to take out parts that it can do internally.
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For example, if the engine can return results sorted according to
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the specified order_by clause, it sets Query::order_by=NULL before
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returning.
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At the moment the engine must take group_by (or return an error), and
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optionally can take distinct, where, order_by, and having.
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The engine should not modify the select list. It is the extended SELECT
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clause (extended, because it has more items than the original
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user-specified SELECT clause) and it contains all aggregate functions,
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used in the query.
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*/
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struct Query
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{
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List<Item> *select;
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bool distinct;
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TABLE_LIST *from;
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Item *where;
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ORDER *group_by;
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ORDER *order_by;
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Item *having;
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// LIMIT
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Select_limit_counters *limit;
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};
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class group_by_handler
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{
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public:
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THD *thd;
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handlerton *ht;
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/*
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Temporary table where all results should be stored in record[0]
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The table has a field for every item from the Query::select list.
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*/
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TABLE *table;
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group_by_handler(THD *thd_arg, handlerton *ht_arg)
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: thd(thd_arg), ht(ht_arg), table(0) {}
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virtual ~group_by_handler() {}
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/*
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Functions to scan data. All these returns 0 if ok, error code in case
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of error
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*/
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/*
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Initialize group_by scan, prepare for next_row().
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If this is a sub query with group by, this can be called many times for
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a query.
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*/
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virtual int init_scan()= 0;
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/*
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Return next group by result in table->record[0].
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Return 0 if row found, HA_ERR_END_OF_FILE if last row and other error
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number in case of fatal error.
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*/
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virtual int next_row()= 0;
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/* End scanning */
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virtual int end_scan()=0;
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/* Report errors */
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virtual void print_error(int error, myf errflag);
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};
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#endif //GROUP_BY_HANDLER_INCLUDED
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