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sql_union.cpp：源码内容
							/* Copyright (C) 2000-2003 MySQL AB
   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; either version 2 of the License, or
   (at your option) any later version.
   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., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA */
/*
  UNION  of select's
  UNION's  were introduced by Monty and Sinisa <sinisa@mysql.com>
*/
#include "mysql_priv.h"
#include "sql_select.h"
int mysql_union(THD *thd, LEX *lex, select_result *result,
		SELECT_LEX_UNIT *unit)
{
  DBUG_ENTER("mysql_union");
  int res= 0;
  if (!(res= unit->prepare(thd, result, SELECT_NO_UNLOCK, "")))
    res= unit->exec();
  res|= unit->cleanup();
  DBUG_RETURN(res);
}
/***************************************************************************
** store records in temporary table for UNION
***************************************************************************/
select_union::select_union(TABLE *table_par)
  :table(table_par)
{
  bzero((char*) &info,sizeof(info));
  /*
    We can always use IGNORE because the temporary table will only
    contain a unique key if we are using not using UNION ALL
  */
  info.ignore= 1;
}
select_union::~select_union()
{
}
int select_union::prepare(List<Item> &list, SELECT_LEX_UNIT *u)
{
  unit= u;
  return 0;
}
bool select_union::send_data(List<Item> &values)
{
  if (unit->offset_limit_cnt)
  {						// using limit offset,count
    unit->offset_limit_cnt--;
    return 0;
  }
  fill_record(table->field, values, 1);
  if (thd->net.report_error || write_record(table,&info))
  {
    if (thd->net.last_errno == ER_RECORD_FILE_FULL)
    {
      thd->clear_error(); // do not report user about table overflow
      if (create_myisam_from_heap(thd, table, &tmp_table_param,
				  info.last_errno, 1))
	return 1;
    }
    else
      return 1;
  }
  return 0;
}
bool select_union::send_eof()
{
  return 0;
}
bool select_union::flush()
{
  int error;
  if ((error=table->file->extra(HA_EXTRA_NO_CACHE)))
  {
    table->file->print_error(error,MYF(0));
    ::send_error(thd);
    return 1;
  }
  return 0;
}
/*
  initialization procedures before fake_select_lex preparation()
  SYNOPSIS
    st_select_lex_unit::init_prepare_fake_select_lex()
    thd		- thread handler
  RETURN
    options of SELECT
*/
ulong
st_select_lex_unit::init_prepare_fake_select_lex(THD *thd) 
{
  ulong options_tmp= thd->options | fake_select_lex->options;
  thd->lex->current_select= fake_select_lex;
  offset_limit_cnt= global_parameters->offset_limit;
  select_limit_cnt= global_parameters->select_limit +
    global_parameters->offset_limit;
  if (select_limit_cnt < global_parameters->select_limit)
    select_limit_cnt= HA_POS_ERROR;		// no limit
  if (select_limit_cnt == HA_POS_ERROR)
    options_tmp&= ~OPTION_FOUND_ROWS;
  else if (found_rows_for_union && !thd->lex->describe)
    options_tmp|= OPTION_FOUND_ROWS;
  fake_select_lex->table_list.link_in_list((byte *)&result_table_list,
					   (byte **)
					   &result_table_list.next);
  return options_tmp;
}
int st_select_lex_unit::prepare(THD *thd_arg, select_result *sel_result,
				ulong additional_options,
                                const char *tmp_table_alias)
{
  SELECT_LEX *lex_select_save= thd_arg->lex->current_select;
  SELECT_LEX *sl, *first_select;
  select_result *tmp_result;
  bool is_union;
  TABLE *empty_table= 0;
  DBUG_ENTER("st_select_lex_unit::prepare");
  describe= test(additional_options & SELECT_DESCRIBE);
  /*
    result object should be reassigned even if preparing already done for
    max/min subquery (ALL/ANY optimization)
  */
  result= sel_result;
  if (prepared)
  {
    if (describe)
    {
      /* fast reinit for EXPLAIN */
      for (sl= first_select_in_union(); sl; sl= sl->next_select())
      {
	sl->join->result= result;
	select_limit_cnt= HA_POS_ERROR;
	offset_limit_cnt= 0;
	if (!sl->join->procedure &&
	    result->prepare(sl->join->fields_list, this))
	{
	  DBUG_RETURN(1);
	}
	sl->join->select_options|= SELECT_DESCRIBE;
	sl->join->reinit();
      }
    }
    DBUG_RETURN(0);
  }
  prepared= 1;
  res= 0;
  
  thd_arg->lex->current_select= sl= first_select= first_select_in_union();
  found_rows_for_union= first_select->options & OPTION_FOUND_ROWS;
  is_union= test(first_select->next_select());
  /* Global option */
  if (is_union)
  {
    if (!(tmp_result= union_result= new select_union(0)))
      goto err;
    union_result->tmp_table_param.init();
    if (describe)
      tmp_result= sel_result;
  }
  else
    tmp_result= sel_result;
  for (;sl; sl= sl->next_select())
  {
    bool can_skip_order_by;
    sl->options|=  SELECT_NO_UNLOCK;
    JOIN *join= new JOIN(thd_arg, sl->item_list, 
			 sl->options | thd_arg->options | additional_options,
			 tmp_result);
    if (!join)
      goto err;
    thd_arg->lex->current_select= sl;
    offset_limit_cnt= sl->offset_limit;
    select_limit_cnt= sl->select_limit+sl->offset_limit;
    if (select_limit_cnt < sl->select_limit)
      select_limit_cnt= HA_POS_ERROR;		// no limit
    can_skip_order_by= is_union &&
                       (!sl->braces || select_limit_cnt == HA_POS_ERROR);
    res= join->prepare(&sl->ref_pointer_array,
		       (TABLE_LIST*) sl->table_list.first, sl->with_wild,
		       sl->where,
                       (can_skip_order_by ? 0 : sl->order_list.elements) +
                       sl->group_list.elements,
                       can_skip_order_by ?
                       (ORDER*) 0 : (ORDER *)sl->order_list.first,
		       (ORDER*) sl->group_list.first,
		       sl->having,
		       (is_union ? (ORDER*) 0 :
                        (ORDER*) thd_arg->lex->proc_list.first),
		       sl, this);
    /* There are no * in the statement anymore (for PS) */
    sl->with_wild= 0;
    last_procedure= join->procedure;
    if (res || thd_arg->is_fatal_error)
      goto err;
    if (sl == first_select)
    {
      /*
        We need to create an empty table object. It is used
        to create tmp_table fields in Item_type_holder.
        The main reason of this is that we can't create
        field object without table.
      */
      DBUG_ASSERT(!empty_table);
      empty_table= (TABLE*) thd->calloc(sizeof(TABLE));
      types.empty();
      List_iterator_fast<Item> it(sl->item_list);
      Item *item_tmp;
      while ((item_tmp= it++))
      {
	/* Error's in 'new' will be detected after loop */
	types.push_back(new Item_type_holder(thd_arg, item_tmp));
      }
      if (thd_arg->is_fatal_error)
	goto err; // out of memory
    }
    else
    {
      if (types.elements != sl->item_list.elements)
      {
	my_message(ER_WRONG_NUMBER_OF_COLUMNS_IN_SELECT,
		   ER(ER_WRONG_NUMBER_OF_COLUMNS_IN_SELECT),MYF(0));
	goto err;
      }
      List_iterator_fast<Item> it(sl->item_list);
      List_iterator_fast<Item> tp(types);	
      Item *type, *item_tmp;
      while ((type= tp++, item_tmp= it++))
      {
        if (((Item_type_holder*)type)->join_types(thd_arg, item_tmp))
	  DBUG_RETURN(-1);
      }
    }
  }
  if (is_union)
  {
    /*
      Check that it was possible to aggregate
      all collations together for UNION.
    */
    List_iterator_fast<Item> tp(types);
    Item_arena *arena= thd->current_arena;
    Item *type;
    ulong create_options;
    while ((type= tp++))
    {
      if (type->result_type() == STRING_RESULT &&
          type->collation.derivation == DERIVATION_NONE)
      {
        my_error(ER_CANT_AGGREGATE_NCOLLATIONS, MYF(0), "UNION");
        goto err;
      }
    }
    
    create_options= (first_select_in_union()->options | thd_arg->options |
                     TMP_TABLE_ALL_COLUMNS);
    /*
      Force the temporary table to be a MyISAM table if we're going to use
      fullext functions (MATCH ... AGAINST .. IN BOOLEAN MODE) when reading
      from it (this should be removed in 5.2 when fulltext search is moved 
      out of MyISAM).
    */
    if (global_parameters->ftfunc_list->elements)
      create_options= create_options | TMP_TABLE_FORCE_MYISAM;
    union_result->tmp_table_param.field_count= types.elements;
    if (!(table= create_tmp_table(thd_arg,
				  &union_result->tmp_table_param, types,
				  (ORDER*) 0, (bool) union_distinct, 1, 
                                  create_options, HA_POS_ERROR, 
                                  (char *) tmp_table_alias)))
      goto err;
    table->file->extra(HA_EXTRA_WRITE_CACHE);
    table->file->extra(HA_EXTRA_IGNORE_DUP_KEY);
    bzero((char*) &result_table_list, sizeof(result_table_list));
    result_table_list.db= (char*) "";
    result_table_list.real_name= result_table_list.alias= (char*) "union";
    result_table_list.table= table;
    union_result->set_table(table);
    thd_arg->lex->current_select= lex_select_save;
    if (!item_list.elements)
    {
      /*
        We're in statement prepare or in execution
        of a conventional statement.
      */
      Item_arena *tmp_arena,backup;
      tmp_arena= thd->change_arena_if_needed(&backup);
      Field **field;
      for (field= table->field; *field; field++)
      {
	Item_field *item= new Item_field(*field);
	if (!item || item_list.push_back(item))
	{
          if (tmp_arena)
	    thd->restore_backup_item_arena(tmp_arena, &backup);
	  DBUG_RETURN(-1);
	}
      }
      if (tmp_arena)
        thd->restore_backup_item_arena(tmp_arena, &backup);
      if (arena->is_stmt_prepare())
      {
	/* prepare fake select to initialize it correctly */
	(void) init_prepare_fake_select_lex(thd);
	if (!(fake_select_lex->join= new JOIN(thd, item_list, thd->options,
					      result)))
	{
	  fake_select_lex->table_list.empty();
	  DBUG_RETURN(-1);
	}
	fake_select_lex->item_list= item_list;
	thd_arg->lex->current_select= fake_select_lex;
	res= fake_select_lex->join->
	  prepare(&fake_select_lex->ref_pointer_array,
		  (TABLE_LIST*) fake_select_lex->table_list.first,
		  0, 0,
		  fake_select_lex->order_list.elements,
		  (ORDER*) fake_select_lex->order_list.first,
		  (ORDER*) NULL, NULL,
                  (ORDER*) NULL,
		  fake_select_lex, this);
	fake_select_lex->table_list.empty();
      }
    }
    else if (arena->is_stmt_execute())
    {
      /*
        We're in execution of a prepared statement: reset field items
        to point at fields from the created temporary table.
      */
      List_iterator_fast<Item> it(item_list);
      for (Field **field= table->field; *field; field++)
      {
        Item_field *item_field= (Item_field*) it++;
        DBUG_ASSERT(item_field);
        item_field->reset_field(*field);
      }
    }
  }
  thd_arg->lex->current_select= lex_select_save;
  DBUG_RETURN(res || thd_arg->is_fatal_error ? 1 : 0);
err:
  thd_arg->lex->current_select= lex_select_save;
  DBUG_RETURN(-1);
}
int st_select_lex_unit::exec()
{
  SELECT_LEX *lex_select_save= thd->lex->current_select;
  SELECT_LEX *select_cursor=first_select_in_union();
  ulonglong add_rows=0;
  ha_rows examined_rows= 0;
  DBUG_ENTER("st_select_lex_unit::exec");
  if (executed && !uncacheable && !describe)
    DBUG_RETURN(0);
  executed= 1;
  
  if (uncacheable || !item || !item->assigned() || describe)
  {
    if (item)
      item->reset_value_registration();
    if (optimized && item)
    {
      if (item->assigned())
      {
        item->assigned(0); // We will reinit & rexecute unit
        item->reset();
        table->file->delete_all_rows();
      }
      /* re-enabling indexes for next subselect iteration */
      if (union_distinct && table->file->enable_indexes(HA_KEY_SWITCH_ALL))
        DBUG_ASSERT(0);
    }
    for (SELECT_LEX *sl= select_cursor; sl; sl= sl->next_select())
    {
      ha_rows records_at_start= 0;
      thd->lex->current_select= sl;
      if (optimized)
	res= sl->join->reinit();
      else
      {
	if (sl != global_parameters && !describe)
	{
	  offset_limit_cnt= sl->offset_limit;
	  select_limit_cnt= sl->select_limit+sl->offset_limit;
	}
	else
	{
	  offset_limit_cnt= 0;
	  /*
	    We can't use LIMIT at this stage if we are using ORDER BY for the
	    whole query
	  */
	  if (sl->order_list.first || describe)
	    select_limit_cnt= HA_POS_ERROR;
	  else
	    select_limit_cnt= sl->select_limit+sl->offset_limit;
	}
	if (select_limit_cnt < sl->select_limit)
	  select_limit_cnt= HA_POS_ERROR;		// no limit
        /*
          When using braces, SQL_CALC_FOUND_ROWS affects the whole query:
          we don't calculate found_rows() per union part.
          Otherwise, SQL_CALC_FOUND_ROWS should be done on all sub parts.
        */
        sl->join->select_options= 
          (select_limit_cnt == HA_POS_ERROR || sl->braces) ?
          sl->options & ~OPTION_FOUND_ROWS : sl->options | found_rows_for_union;
	res= sl->join->optimize();
      }
      if (!res)
      {
	records_at_start= table->file->records;
	sl->join->exec();
        if (sl == union_distinct)
	{
	  if (table->file->disable_indexes(HA_KEY_SWITCH_ALL))
	    DBUG_RETURN(1);
	  table->no_keyread=1;
	}
	res= sl->join->error;
	offset_limit_cnt= sl->offset_limit;
	if (!res)
	{
	  examined_rows+= thd->examined_row_count;
	  if (union_result->flush())
	  {
	    thd->lex->current_select= lex_select_save;
	    DBUG_RETURN(1);
	  }
	}
      }
      if (res)
      {
	thd->lex->current_select= lex_select_save;
	DBUG_RETURN(res);
      }
      /* Needed for the following test and for records_at_start in next loop */
      table->file->info(HA_STATUS_VARIABLE);
      if (found_rows_for_union && !sl->braces && 
          select_limit_cnt != HA_POS_ERROR)
      {
	/*
	  This is a union without braces. Remember the number of rows that
	  could also have been part of the result set.
	  We get this from the difference of between total number of possible
	  rows and actual rows added to the temporary table.
	*/
	add_rows+= (ulonglong) (thd->limit_found_rows - (ulonglong)
			      ((table->file->records -  records_at_start)));
      }
    }
  }
  optimized= 1;
  /* Send result to 'result' */
  res= -1;
  {
    List<Item_func_match> empty_list;
    empty_list.empty();
    if (!thd->is_fatal_error)				// Check if EOM
    {
      ulong options_tmp= init_prepare_fake_select_lex(thd);
      JOIN *join= fake_select_lex->join;
      if (!join)
      {
	/*
	  allocate JOIN for fake select only once (prevent
	  mysql_select automatic allocation)
	*/
	if (!(fake_select_lex->join= new JOIN(thd, item_list, thd->options,
					      result)))
	{
	  fake_select_lex->table_list.empty();
	  DBUG_RETURN(-1);
	}
	/*
	  Fake st_select_lex should have item list for correctref_array
	  allocation.
	*/
	fake_select_lex->item_list= item_list;
      }
      else
      {
	JOIN_TAB *tab,*end;
	for (tab=join->join_tab,end=tab+join->tables ; tab != end ; tab++)
	{
	  delete tab->select;
	  delete tab->quick;
	}
	join->init(thd, item_list, thd->options, result);
      }
      res= mysql_select(thd, &fake_select_lex->ref_pointer_array,
			&result_table_list,
			0, item_list, NULL,
			global_parameters->order_list.elements,
			(ORDER*)global_parameters->order_list.first,
			(ORDER*) NULL, NULL, (ORDER*) NULL,
			options_tmp | SELECT_NO_UNLOCK,
			result, this, fake_select_lex);
      fake_select_lex->table_list.empty();
      if (!res)
      {
	thd->limit_found_rows = (ulonglong)table->file->records + add_rows;
        thd->examined_row_count+= examined_rows;
      }
      /*
	Mark for slow query log if any of the union parts didn't use
	indexes efficiently
      */
    }
  }
  thd->lex->current_select= lex_select_save;
  DBUG_RETURN(res);
}
int st_select_lex_unit::cleanup()
{
  int error= 0;
  DBUG_ENTER("st_select_lex_unit::cleanup");
  if (cleaned)
  {
    DBUG_RETURN(0);
  }
  cleaned= 1;
  if (union_result)
  {
    delete union_result;
    union_result=0; // Safety
    if (table)
      free_tmp_table(thd, table);
    table= 0; // Safety
  }
  JOIN *join;
  SELECT_LEX *sl= first_select_in_union();
  for (; sl; sl= sl->next_select())
  {
    if ((join= sl->join))
    {
      error|= sl->join->cleanup();
      delete join;
    }
    else
    {
      // it can be DO/SET with subqueries
      for (SELECT_LEX_UNIT *lex_unit= sl->first_inner_unit();
	   lex_unit != 0;
	   lex_unit= lex_unit->next_unit())
      {
	error|= lex_unit->cleanup();
      }
    }
  }
  if (fake_select_lex && (join= fake_select_lex->join))
  {
    join->tables_list= 0;
    join->tables= 0;
    error|= join->cleanup();
    delete join;
  }
  DBUG_RETURN(error);
}
void st_select_lex_unit::reinit_exec_mechanism()
{
  prepared= optimized= executed= 0;
#ifndef DBUG_OFF
  if (first_select()->next_select())
  {
    List_iterator_fast<Item> it(item_list);
    Item *field;
    while ((field= it++))
    {
      /*
	we can't cleanup here, because it broke link to temporary table field,
	but have to drop fixed flag to allow next fix_field of this field
	during re-executing
      */
      field->fixed= 0;
    }
  }
#endif
}
/*
  change select_result object of unit
  SYNOPSIS
    st_select_lex_unit::change_result()
    result	new select_result object
    old_result	old select_result object
  RETURN
    0 - OK
    -1 - error
*/
int st_select_lex_unit::change_result(select_subselect *result,
				      select_subselect *old_result)
{
  int res= 0;
  for (SELECT_LEX *sl= first_select_in_union(); sl; sl= sl->next_select())
  {
    if (sl->join && sl->join->result == old_result)
      if ((res= sl->join->change_result(result)))
	return (res);
  }
  if (fake_select_lex && fake_select_lex->join)
    res= fake_select_lex->join->change_result(result);
  return (res);
}

						