opt_explain.h

/* Copyright (c) 2011, 2012, Oracle and/or its affiliates. All rights reserved.

   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,
   51 Franklin Street, Suite 500, Boston, MA 02110-1335 USA */


#ifndef OPT_EXPLAIN_INCLUDED
#define OPT_EXPLAIN_INCLUDED

/** @file "EXPLAIN <command>" 

Single table UPDATE/DELETE commands are explained by the 
explain_single_table_modification() function.

A query expression (complete SELECT query possibly including
subqueries and unions), INSERT...SELECT and multitable UPDATE/DELETE
commands are explained like this:

(1) explain_query_expression()

Is the entry point. Forwards the job to explain_unit().

(2) explain_unit()

Is for a SELECT_LEX_UNIT, prepares, optimizes, explains one JOIN for
each "top-level" SELECT_LEXs of the unit (like: all SELECTs of a
UNION; but not subqueries), and one JOIN for the fake SELECT_LEX of
UNION); each JOIN explain (JOIN::exec()) calls explain_query_specification()

(3) explain_query_specification()

Is for a single SELECT_LEX (fake or not). It needs a prepared and
optimized JOIN, for which it builds the EXPLAIN rows. But it also
launches the EXPLAIN process for "inner units" (==subqueries of this
SELECT_LEX), by calling explain_unit() for each of them. 
*/

#include <my_base.h>

class JOIN;
class select_result;
class select_result_interceptor;
class SQL_SELECT;
struct TABLE;
class THD;


extern const char *join_type_str[];

bool explain_no_table(THD *thd, JOIN *join, const char *message);
bool explain_no_table(THD *thd, const char *message,
                      ha_rows rows= HA_POS_ERROR);
bool explain_single_table_modification(THD *thd,
                                       TABLE *table,
                                       const SQL_SELECT *select,
                                       uint key,
                                       ha_rows limit,
                                       bool need_tmp_table,
                                       bool need_sort,
                                       bool is_update,
                                       bool used_key_is_modified= false);
bool explain_query_specification(THD *thd, JOIN *join);
bool explain_multi_table_modification(THD *thd,
                                      select_result_interceptor *result);
bool explain_query_expression(THD *thd, select_result *result);

#endif /* OPT_EXPLAIN_INCLUDED */