sql_derived.cc

/* Copyright (C) 2000 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 */


/*
  Derived tables
  These were introduced by Monty and Sinisa <sinisa@mysql.com>
*/


#include "mysql_priv.h"
#include "sql_select.h"
#include "sql_acl.h"

static const char *any_db="*any*";	// Special symbol for check_access

/*
  Resolve derived tables in all queries

  SYNOPSIS
    mysql_derived(THD *thd, LEX *lex, SELECT_LEX_UNIT *unit, TABLE_LIST *t)
    thd			Thread handle
    lex                 LEX for this thread
    unit                node that contains all SELECT's for derived tables
    t                   TABLE_LIST for the upper SELECT

  IMPLEMENTATION
  
  Derived table is  resolved with temporary table. It is created based on the
  queries defined. After temporary table is created, if this is not EXPLAIN,
  then the entire unit / node is deleted. unit is deleted if UNION is used 
  for derived table and node is deleted is it is a  simple SELECT.

  After table creation, the above TABLE_LIST is updated with a new table.

  This function is called before any command containing derived table is executed. 

  TODO: To move creation of derived tables IN  open_and_lock_tables()
*/  


int mysql_derived(THD *thd, LEX *lex, SELECT_LEX_UNIT *unit, TABLE_LIST *t)
{
  SELECT_LEX *sl= unit->first_select();
  List<Item> item_list;
  TABLE *table;
  int res= 0;
  select_union *derived_result;
  TABLE_LIST *tables= (TABLE_LIST *)sl->table_list.first;
  TMP_TABLE_PARAM tmp_table_param;
  bool is_union=sl->next_select() && sl->next_select()->linkage == UNION_TYPE;
  DBUG_ENTER("mysql_derived");
  

/*
  In create_total_list, derived tables have to be treated in case of EXPLAIN, 
  This is because unit/node is not deleted in that case. Current code in this 
  function has to be improved to recognize better when this function is called 
  from derived tables and when from other functions.
*/
  if (is_union && unit->create_total_list(thd, lex, &tables))
    DBUG_RETURN(-1);

  if (tables)
    res= check_table_access(thd,SELECT_ACL, tables);
  else
    res= check_access(thd, SELECT_ACL, any_db);
  if (res)
    DBUG_RETURN(-1);

  Item *item;
  List_iterator<Item> it(sl->item_list);

  while ((item= it++))
    item_list.push_back(item);
    
  if (!(res=open_and_lock_tables(thd,tables)))
  {
    if (is_union)
    {
/* 
   The following code is a re-do of fix_tables_pointers() found in sql_select.cc
   for UNION's within derived tables. The only difference is in navigation, as in 
   derived tables we care for this level only.

   fix_tables_pointers makes sure that in UNION's we do not open single table twice 
   if found in different SELECT's.

*/
      for (SELECT_LEX *sel= sl;
	   sel;
	   sel= sel->next_select())
      {
	for (TABLE_LIST *cursor= (TABLE_LIST *)sel->table_list.first;
	     cursor;
	     cursor=cursor->next)
	  cursor->table= cursor->table_list->table;
      }
    }

    if (setup_fields(thd,tables,item_list,0,0,1))
    {
      res=-1;
      goto exit;
    }
    bzero((char*) &tmp_table_param,sizeof(tmp_table_param));
    tmp_table_param.field_count=item_list.elements;
    if (!(table=create_tmp_table(thd, &tmp_table_param, item_list,
			         (ORDER*) 0, is_union && !unit->union_option, 1,
			         (sl->options | thd->options |
				  TMP_TABLE_ALL_COLUMNS),
                                 HA_POS_ERROR)))
    {
      res=-1;
      goto exit;
    }
  
    if ((derived_result=new select_union(table)))
    {
      derived_result->tmp_table_param=&tmp_table_param;
      unit->offset_limit_cnt= sl->offset_limit;
      unit->select_limit_cnt= sl->select_limit+sl->offset_limit;
      if (unit->select_limit_cnt < sl->select_limit)
	unit->select_limit_cnt= HA_POS_ERROR;
      if (unit->select_limit_cnt == HA_POS_ERROR)
	sl->options&= ~OPTION_FOUND_ROWS;

      SELECT_LEX_NODE *save_current_select= lex->current_select;
      lex->current_select= sl;
      if (is_union)
	res=mysql_union(thd,lex,derived_result,unit);
      else
	res= mysql_select(thd, tables,  sl->item_list,
			sl->where, (ORDER *) sl->order_list.first,
			(ORDER*) sl->group_list.first,
			sl->having, (ORDER*) NULL,
			sl->options | thd->options  | SELECT_NO_UNLOCK,
			derived_result, unit, sl, 0);
      lex->current_select= save_current_select;

      if (!res)
      {
// Here we entirely fix both TABLE_LIST and list of SELECT's as there were no derived tables
	if (derived_result->flush())
	  res=1;
	else
	{
	  t->real_name=table->real_name;
	  t->table=table;
	  table->derived_select_number= sl->select_number;
	  table->tmp_table=TMP_TABLE;
	  if (lex->describe)
	  {
	    if (tables)
	      tables->table_list->table=tables->table; // to fix a problem in EXPLAIN
	  }
	  else
	    unit->exclude();
	  t->db=(char *)"";
	  t->derived=(SELECT_LEX *)1; // just in case ...
	  table->file->info(HA_STATUS_VARIABLE);
	}
      }
      delete derived_result;
    }
    if (res)
      free_tmp_table(thd,table);
exit:
    close_thread_tables(thd);
  }
  DBUG_RETURN(res);
}