mysql-5.6.51/sql/sql_union.cc

/* Copyright (c) 2001, 2017, 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, version 2.0,
   as published by the Free Software Foundation.

   This program is also distributed with certain software (including
   but not limited to OpenSSL) that is licensed under separate terms,
   as designated in a particular file or component or in included license
   documentation.  The authors of MySQL hereby grant you an additional
   permission to link the program and your derivative works with the
   separately licensed software that they have included with MySQL.

   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, version 2.0, 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 St, Fifth Floor, Boston, MA  02110-1301  USA */

/*
  UNION  of select's
  UNION's  were introduced by Monty and Sinisa <sinisa@mysql.com>
*/


#include "sql_priv.h"
#include "unireg.h"
#include "sql_union.h"
#include "sql_select.h"
#include "sql_cursor.h"
#include "sql_base.h"                           // fill_record
#include "filesort.h"                           // filesort_free_buffers
#include "sql_tmp_table.h"                      // tmp tables
#include "sql_optimizer.h"                      // JOIN
#include "opt_explain_format.h"

bool mysql_union(THD *thd, LEX *lex, select_result *result,
                 SELECT_LEX_UNIT *unit, ulong setup_tables_done_option)
{
  bool res;
  DBUG_ENTER("mysql_union");

  res= unit->prepare(thd, result,
		     SELECT_NO_UNLOCK | setup_tables_done_option);
  if (res)
    goto err;


  /*
    Tables are not locked at this point, it means that we have delayed
    this step until after prepare stage (i.e. this moment). This allows to
    do better partition pruning and avoid locking unused partitions.
    As a consequence, in such a case, prepare stage can rely only on
    metadata about tables used and not data from them.
    We need to lock tables now in order to proceed with the remaning
    stages of query optimization and execution.
  */
  DBUG_ASSERT(! thd->lex->is_query_tables_locked());
  if (lock_tables(thd, lex->query_tables, lex->table_count, 0))
    goto err;

  /*
    Tables must be locked before storing the query in the query cache.
    Transactional engines must been signalled that the statement started,
    which external_lock signals.
  */
  query_cache_store_query(thd, thd->lex->query_tables);

  res= unit->optimize() || unit->exec();
  res|= unit->cleanup();
  DBUG_RETURN(res);
err:
  (void) unit->cleanup();
  DBUG_RETURN(true);
}


/***************************************************************************
** store records in temporary table for UNION
***************************************************************************/

int select_union::prepare(List<Item> &list, SELECT_LEX_UNIT *u)
{
  unit= u;
  return 0;
}


bool select_union::send_data(List<Item> &values)
{
  int error= 0;
  if (unit->offset_limit_cnt)
  {						// using limit offset,count
    unit->offset_limit_cnt--;
    return 0;
  }
  fill_record(thd, table->field, values, 1, NULL);
  if (thd->is_error())
    return 1;

  if ((error= table->file->ha_write_row(table->record[0])))
  {
    /* create_myisam_from_heap will generate error if needed */
    if (table->file->is_fatal_error(error, HA_CHECK_DUP) &&
        create_myisam_from_heap(thd, table, tmp_table_param.start_recinfo,
                                &tmp_table_param.recinfo, error, TRUE, NULL))
      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));
    return 1;
  }
  return 0;
}

/*
  Create a temporary table to store the result of select_union.

  SYNOPSIS
    select_union::create_result_table()
      thd                thread handle
      column_types       a list of items used to define columns of the
                         temporary table
      is_union_distinct  if set, the temporary table will eliminate
                         duplicates on insert
      options            create options
      table_alias        name of the temporary table
      bit_fields_as_long convert bit fields to ulonglong

  DESCRIPTION
    Create a temporary table that is used to store the result of a UNION,
    derived table, or a materialized cursor.

  RETURN VALUE
    0                    The table has been created successfully.
    1                    create_tmp_table failed.
*/

bool
select_union::create_result_table(THD *thd_arg, List<Item> *column_types,
                                  bool is_union_distinct, ulonglong options,
                                  const char *table_alias,
                                  bool bit_fields_as_long, bool create_table)
{
  DBUG_ASSERT(table == 0);
  tmp_table_param.init();
  tmp_table_param.field_count= column_types->elements;
  tmp_table_param.skip_create_table= !create_table;
  tmp_table_param.bit_fields_as_long= bit_fields_as_long;

  if (! (table= create_tmp_table(thd_arg, &tmp_table_param, *column_types,
                                 (ORDER*) 0, is_union_distinct, 1,
                                 options, HA_POS_ERROR, (char*) table_alias)))
    return TRUE;
  if (create_table)
  {
    table->file->extra(HA_EXTRA_WRITE_CACHE);
    table->file->extra(HA_EXTRA_IGNORE_DUP_KEY);
  }
  return FALSE;
}


/**
  Reset and empty the temporary table that stores the materialized query result.

  @note The cleanup performed here is exactly the same as for the two temp
  tables of JOIN - exec_tmp_table_[1 | 2].
*/

void select_union::cleanup()
{
  table->file->extra(HA_EXTRA_RESET_STATE);
  table->file->ha_delete_all_rows();
  free_io_cache(table);
  filesort_free_buffers(table,0);
}


/**
  Initialization procedures before fake_select_lex preparation()

  @param thd		 Thread handler
  @param no_const_tables Skip reading const tables. TRUE for EXPLAIN.

  @returns
    TRUE  OOM
    FALSE Ok
*/

bool
st_select_lex_unit::init_prepare_fake_select_lex(THD *thd_arg,
                                                 bool no_const_tables)
{
  DBUG_ENTER("st_select_lex_unit::init_prepare_fake_select_lex");
  thd_arg->lex->current_select= fake_select_lex;
  fake_select_lex->table_list.link_in_list(&result_table_list,
                                           &result_table_list.next_local);
  fake_select_lex->context.table_list=
    fake_select_lex->context.first_name_resolution_table=
    fake_select_lex->get_table_list();
  if (!fake_select_lex->first_execution)
  {
    for (ORDER *order= global_parameters->order_list.first;
         order;
         order= order->next)
      order->item= &order->item_ptr;
  }
  for (ORDER *order= global_parameters->order_list.first;
       order;
       order=order->next)
  {
    (*order->item)->walk(&Item::change_context_processor, 0,
                         (uchar*) &fake_select_lex->context);
  }
  if (!fake_select_lex->join)
  {
    /*
      allocate JOIN for fake select only once (prevent
      mysql_select automatic allocation)
      TODO: The above is nonsense. mysql_select() will not allocate the
      join if one already exists. There must be some other reason why we
      don't let it allocate the join. Perhaps this is because we need
      some special parameter values passed to join constructor?
    */
    if (!(fake_select_lex->join=
        new JOIN(thd, item_list, fake_select_lex->options, result)))
    {
      fake_select_lex->table_list.empty();
      DBUG_RETURN(true);
    }
    fake_select_lex->join->init(thd, item_list, fake_select_lex->options,
                                result);
    fake_select_lex->join->no_const_tables= no_const_tables;

    /*
      Fake st_select_lex should have item list for correct ref_array
      allocation.
    */
    fake_select_lex->item_list= item_list;

    /*
      We need to add up n_sum_items in order to make the correct
      allocation in setup_ref_array().
      Don't add more sum_items if we have already done JOIN::prepare
      for this (with a different join object)
    */
    if (fake_select_lex->ref_pointer_array.is_null())
      fake_select_lex->n_child_sum_items+= global_parameters->n_sum_items;
  }
  DBUG_RETURN(false);
}


bool st_select_lex_unit::prepare(THD *thd_arg, select_result *sel_result,
                                 ulong additional_options)
{
  SELECT_LEX *lex_select_save= thd_arg->lex->current_select;
  SELECT_LEX *sl, *first_sl= first_select();
  select_result *tmp_result;
  bool is_union_select;
  DBUG_ENTER("st_select_lex_unit::prepare");

  describe= MY_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_sl; sl; sl= sl->next_select())
      {
        sl->join->result= result;
        select_limit_cnt= HA_POS_ERROR;
        offset_limit_cnt= 0;
        if (result->prepare(sl->join->fields_list, this))
        {
          DBUG_RETURN(TRUE);
        }
        sl->join->select_options|= SELECT_DESCRIBE;
        sl->join->reset();
      }
      if (fake_select_lex->join)
        fake_select_lex->join->result= result;
    }
    DBUG_RETURN(FALSE);
  }
  prepared= 1;
  saved_error= FALSE;

  thd_arg->lex->current_select= sl= first_sl;
  found_rows_for_union= first_sl->options & OPTION_FOUND_ROWS;
  is_union_select= is_union() || fake_select_lex;

  /* Global option */

  if (is_union_select)
  {
    if (!(tmp_result= union_result= new select_union))
      goto err;
    if (describe)
      tmp_result= sel_result;
  }
  else
    tmp_result= sel_result;

  sl->context.resolve_in_select_list= TRUE;

  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->variables.option_bits | additional_options,
			 tmp_result);
    /*
      setup_tables_done_option should be set only for very first SELECT,
      because it protect from secont setup_tables call for select-like non
      select commands (DELETE/INSERT/...) and they use only very first
      SELECT (for union it can be only INSERT ... SELECT).
    */
    additional_options&= ~OPTION_SETUP_TABLES_DONE;
    if (!join)
      goto err;

    thd_arg->lex->current_select= sl;

    can_skip_order_by= is_union_select && !(sl->braces && sl->explicit_limit);

    saved_error= join->prepare(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 ?
                               NULL : sl->order_list.first,
                               sl->group_list.first,
                               sl->having,
                               sl, this);
    /* There are no * in the statement anymore (for PS) */
    sl->with_wild= 0;

    if (saved_error || (saved_error= thd_arg->is_fatal_error))
      goto err;
    /*
      Use items list of underlaid select for derived tables to preserve
      information about fields lengths and exact types
    */
    if (!is_union_select)
      types= first_sl->item_list;
    else if (sl == first_sl)
    {
      types.empty();
      List_iterator_fast<Item> it(sl->item_list);
      Item *item_tmp;
      while ((item_tmp= it++))
      {
        /*
          If the outer query has a GROUP BY clause, an outer reference to this
          query block may have been wrapped in a Item_outer_ref, which has not
          been fixed yet. An Item_type_holder must be created based on a fixed
          Item, so use the inner Item instead.
        */
        DBUG_ASSERT(item_tmp->fixed ||
                    (item_tmp->type() == Item::REF_ITEM &&
                     ((Item_ref *)(item_tmp))->ref_type() ==
                     Item_ref::OUTER_REF));
        if (!item_tmp->fixed)
          item_tmp= item_tmp->real_item();

	/* 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(TRUE);
      }
    }
  }

  if (is_union_select)
  {
    /*
      Check that it was possible to aggregate
      all collations together for UNION.
      We need this in case of UNION DISTINCT, to filter
      out duplicates using the proper collation.

      TODO: consider removing this test in case of UNION ALL.
    */
    List_iterator_fast<Item> tp(types);
    Item *type;
    ulonglong 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;
      }
    }

    /*
      Disable the usage of fulltext searches in the last union branch.
      This is a temporary 5.x limitation because of the way the fulltext
      search functions are handled by the optimizer.
      This is manifestation of the more general problems of "taking away"
      parts of a SELECT statement post-fix_fields(). This is generally not
      doable since various flags are collected in various places (e.g.
      SELECT_LEX) that carry information about the presence of certain
      expressions or constructs in the parts of the query.
      When part of the query is taken away it's not clear how to "divide"
      the meaning of these accumulated flags and what to carry over to the
      recipient query (SELECT_LEX).
    */
    if (global_parameters->ftfunc_list->elements &&
        global_parameters->order_list.elements &&
        global_parameters != fake_select_lex)
    {
      ORDER *ord;
      Item_func::Functype ft=  Item_func::FT_FUNC;
      for (ord= global_parameters->order_list.first; ord; ord= ord->next)
        if ((*ord->item)->walk (&Item::find_function_processor, FALSE,
                                (uchar *) &ft))
        {
          my_error (ER_CANT_USE_OPTION_HERE, MYF(0), "MATCH()");
          goto err;
        }
    }


    create_options= (first_sl->options | thd_arg->variables.option_bits |
                     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;

    if (union_result->create_result_table(thd, &types, MY_TEST(union_distinct),
                                          create_options, "", FALSE, TRUE))
      goto err;
    memset(&result_table_list, 0, sizeof(result_table_list));
    result_table_list.db= (char*) "";
    result_table_list.table_name= result_table_list.alias= (char*) "union";
    result_table_list.table= table= union_result->table;

    thd_arg->lex->current_select= lex_select_save;
    if (!item_list.elements)
    {
      {
        Prepared_stmt_arena_holder ps_arena_holder(thd);

        saved_error= table->fill_item_list(&item_list);

        if (saved_error)
          goto err;
      }

      if (thd->stmt_arena->is_stmt_prepare())
      {
        /* Validate the global parameters of this union */
        init_prepare_fake_select_lex(thd, false);

	saved_error= fake_select_lex->join->
	  prepare(fake_select_lex->table_list.first, // tables_init
                  0,                                 // wild_num
                  0,                                 // conds_init
                  global_parameters->order_list.elements, // og_num
                  global_parameters->order_list.first,    // order
                  NULL,                                // group_init
                  NULL,                                // having_init
                  fake_select_lex,                     // select_lex_arg
                  this);                               // unit_arg
	fake_select_lex->table_list.empty();
      }
    }
    else
    {
      /*
        We're in execution of a prepared statement or stored procedure:
        reset field items to point at fields from the created temporary table.
      */
      table->reset_item_list(&item_list);
    }
  }

  thd_arg->lex->current_select= lex_select_save;

  DBUG_RETURN(saved_error || thd_arg->is_fatal_error);

err:
  thd_arg->lex->current_select= lex_select_save;
  (void) cleanup();
  DBUG_RETURN(TRUE);
}


/**
  Run optimization phase.

  @return FALSE unit successfully passed optimization phase.
  @return TRUE an error occur.
*/

bool st_select_lex_unit::optimize()
{
  DBUG_ENTER("st_select_lex_unit::optimize");

  if (optimized && item && item->assigned() && !uncacheable && !describe)
    DBUG_RETURN(FALSE);

  for (SELECT_LEX *sl= first_select(); sl; sl= sl->next_select())
  {
    DBUG_ASSERT(sl->join);
    if (optimized)
    {
      saved_error= false;
      sl->join->reset();
    }
    else
    {
      SELECT_LEX *lex_select_save= thd->lex->current_select;
      thd->lex->current_select= sl;
      set_limit(sl);
      if ((sl == global_parameters && is_union()) || describe)
      {
        offset_limit_cnt= 0;
        /*
          We can't use LIMIT at this stage if we are using ORDER BY for the
          whole UNION.
        */
        if (sl->order_list.first || describe)
          select_limit_cnt= HA_POS_ERROR;
      }

      /*
        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;

      saved_error= sl->join->optimize();
      /*
        Accumulate estimated number of rows.
        1. Implicitly grouped query has one row (with HAVING it has zero or one
           rows).
        2. If GROUP BY clause is optimized away because it was a constant then
           query produces at most one row.
      */
      result->estimated_rowcount+=
        (sl->with_sum_func && sl->group_list.elements == 0) ||
        sl->join->group_optimized_away ?
          1 : sl->join->best_rowcount;

      thd->lex->current_select= lex_select_save;
    }
    if (saved_error)
      break;
  }
  if (!saved_error)
    optimized= 1;

  DBUG_RETURN(saved_error);
}


/**
  Explain UNION.
*/

bool st_select_lex_unit::explain()
{
  SELECT_LEX *lex_select_save= thd->lex->current_select;
  Explain_format *fmt= thd->lex->explain_format;
  DBUG_ENTER("st_select_lex_unit::explain");
  JOIN *join;
  bool ret= false;

  DBUG_ASSERT((is_union() || fake_select_lex) && describe && optimized);
  executed= true;

  if (fmt->begin_context(CTX_UNION))
    DBUG_RETURN(true);

  for (SELECT_LEX *sl= first_select(); sl; sl= sl->next_select())
  {
    if (fmt->begin_context(CTX_QUERY_SPEC))
      DBUG_RETURN(true);
    DBUG_ASSERT(sl->join);
    if (sl->join->explain() || thd->is_error())
      DBUG_RETURN(true);
    if (fmt->end_context(CTX_QUERY_SPEC))
      DBUG_RETURN(true);
  }

  if (init_prepare_fake_select_lex(thd, true))
    DBUG_RETURN(true);

  if (thd->is_fatal_error)
    DBUG_RETURN(true);
  join= fake_select_lex->join;

  /*
    In EXPLAIN command, constant subqueries that do not use any
    tables are executed two times:
     - 1st time is a real evaluation to get the subquery value
     - 2nd time is to produce EXPLAIN output rows.
    1st execution sets certain members (e.g. select_result) to perform
    subquery execution rather than EXPLAIN line production. In order
    to reset them back, we re-do all of the actions (yes it is ugly).
  */
  if (!join->optimized || !join->tables)
  {
    saved_error= mysql_select(thd,
                          &result_table_list,
                          0, item_list, NULL,
                          &global_parameters->order_list,
                          NULL, NULL,
                          fake_select_lex->options | SELECT_NO_UNLOCK,
                          result, this, fake_select_lex);
  }
  else
    ret= join->explain();

  thd->lex->current_select= lex_select_save;

  if (saved_error || ret || thd->is_error())
    DBUG_RETURN(true);
  fmt->end_context(CTX_UNION);

  DBUG_RETURN(false);
}


/**
  Execute UNION.
*/

bool st_select_lex_unit::exec()
{
  SELECT_LEX *lex_select_save= thd->lex->current_select;
  ulonglong add_rows=0;
  ha_rows examined_rows= 0;
  DBUG_ENTER("st_select_lex_unit::exec");
  DBUG_ASSERT((is_union() || fake_select_lex) && !describe && optimized);

  if (executed && !uncacheable)
    DBUG_RETURN(false);
  executed= true;

  if (uncacheable || !item || !item->assigned())
  {
    if (item)
      item->reset_value_registration();
    if (optimized && item)
    {
      if (item->assigned())
      {
        item->assigned(0); // We will reinit & rexecute unit
        item->reset();
        table->file->ha_delete_all_rows();
      }
      /* re-enabling indexes for next subselect iteration */
      if (union_distinct && table->file->ha_enable_indexes(HA_KEY_SWITCH_ALL))
      {
        DBUG_ASSERT(0);
      }
    }

    for (SELECT_LEX *sl= first_select(); sl; sl= sl->next_select())
    {
      ha_rows records_at_start= 0;
      DBUG_ASSERT(sl->join);
      thd->lex->current_select= sl;

      set_limit(sl);
      if (sl == global_parameters || describe)
      {
        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;
      }
      if (!saved_error)
      {
        records_at_start= table->file->stats.records;
        sl->join->exec();
        if (sl == union_distinct)
        {
          if (table->file->ha_disable_indexes(HA_KEY_SWITCH_ALL))
            DBUG_RETURN(true);
          table->no_keyread=1;
        }
        saved_error= sl->join->error;
        offset_limit_cnt= (ha_rows)(sl->offset_limit ?
                                    sl->offset_limit->val_uint() :
                                    0);
        if (!saved_error)
        {
          /*
            Save the current examined row count locally and clear the global
            counter, so that we can accumulate the number of evaluated rows for
            the current query block.
          */
	  examined_rows+= thd->get_examined_row_count();
          thd->set_examined_row_count(0);

          if (union_result->flush())
          {
            thd->lex->current_select= lex_select_save;
            DBUG_RETURN(true);
          }
        }
      }
      if (saved_error)
      {
        thd->lex->current_select= lex_select_save;
        DBUG_RETURN(saved_error);
      }
      /* Needed for the following test and for records_at_start in next loop */
      int error= table->file->info(HA_STATUS_VARIABLE);
      if(error)
      {
        table->file->print_error(error, MYF(0));
        DBUG_RETURN(true);
      }
      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->stats.records - records_at_start));
      }
    }
  }

  if (!saved_error && !thd->is_fatal_error)
  {
    /* Send result to 'result' */
    saved_error= true;
    List<Item_func_match> empty_list;
    empty_list.empty();

    set_limit(global_parameters);
    if (init_prepare_fake_select_lex(thd, true))
      DBUG_RETURN(true);
    JOIN *join= fake_select_lex->join;
    if (!join->optimized)
    {
      saved_error=
        mysql_select(thd,
                     &result_table_list,      // tables
                     0,                       // wild_num
                     item_list,               // fields
                     NULL,                    // conds
                     &global_parameters->order_list,    // order
                     NULL,                    // group
                     NULL,                    // having
                     fake_select_lex->options | SELECT_NO_UNLOCK,
                     result,                  // result
                     this,                    // unit
                     fake_select_lex);        // select_lex
    }
    else
    {
      join->examined_rows= 0;
      saved_error= false;
      join->reset();
      join->exec();
    }

    fake_select_lex->table_list.empty();
  }
  if (!saved_error && !thd->is_fatal_error)
  {

    thd->limit_found_rows = (ulonglong)table->file->stats.records + add_rows;
    thd->inc_examined_row_count(examined_rows);
  }
  thd->lex->current_select= lex_select_save;
  DBUG_RETURN(saved_error);
}


/**
  Cleanup this query expression object after preparation or one round
  of execution. After the cleanup, the object can be reused for a
  new round of execution, but a new optimization will be needed before
  the execution.

  @return false if previous execution was successful, and true otherwise
*/

bool st_select_lex_unit::cleanup()
{
  bool error= false;
  DBUG_ENTER("st_select_lex_unit::cleanup");

  if (cleaned)
  {
    DBUG_RETURN(FALSE);
  }
  cleaned= true;

  for (SELECT_LEX *sl= first_select(); sl; sl= sl->next_select())
    error|= sl->cleanup();

  cleanup_level();

  DBUG_RETURN(error);
}


/**
  Cleanup only this select_lex_unit after preparation or one round of
  execution.

  @return false if previous execution was successful, and true otherwise
*/
bool st_select_lex_unit::cleanup_level()
{
  bool error= false;

  if (fake_select_lex)
  {
    error|= fake_select_lex->cleanup();
    /*
      There are two cases when we should clean order items:
      1. UNION with SELECTs which all enclosed into braces
        in this case global_parameters == fake_select_lex
      2. UNION where last SELECT is not enclosed into braces
        in this case global_parameters == 'last select'
      So we should use global_parameters->order_list for
      proper order list clean up.
      Note: global_parameters and fake_select_lex are always
            initialized for UNION
    */
    DBUG_ASSERT(global_parameters);
    if (global_parameters->order_list.elements)
    {
      ORDER *ord;
      for (ord= global_parameters->order_list.first; ord; ord= ord->next)
        (*ord->item)->walk (&Item::cleanup_processor, 0, 0);
    }
  }

  if (union_result)
  {
    delete union_result;
    union_result=0; // Safety
    if (table)
      free_tmp_table(thd, table);
    table= 0; // Safety
  }

  explain_marker= CTX_NONE;

  return error;
}


void st_select_lex_unit::reinit_exec_mechanism()
{
  prepared= optimized= executed= 0;
#ifndef DBUG_OFF
  if (is_union())
  {
    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
    FALSE - OK
    TRUE  - error
*/

bool st_select_lex_unit::change_result(select_result_interceptor *new_result,
                                       select_result_interceptor *old_result)
{
  bool res= FALSE;
  for (SELECT_LEX *sl= first_select(); sl; sl= sl->next_select())
  {
    if (sl->join && sl->join->result == old_result)
      if (sl->join->change_result(new_result))
	return TRUE;
  }
  if (fake_select_lex && fake_select_lex->join)
    res= fake_select_lex->join->change_result(new_result);
  return (res);
}

/*
  Get column type information for this unit.

  SYNOPSIS
    st_select_lex_unit::get_unit_column_types()

  DESCRIPTION
    For a single-select the column types are taken
    from the list of selected items. For a union this function
    assumes that st_select_lex_unit::prepare has been called
    and returns the type holders that were created for unioned
    column types of all selects.

  NOTES
    The implementation of this function should be in sync with
    st_select_lex_unit::prepare()
*/

List<Item> *st_select_lex_unit::get_unit_column_types()
{
  if (is_union())
  {
    DBUG_ASSERT(prepared);
    /* Types are generated during prepare */
    return &types;
  }

  return &first_select()->item_list;
}


/**
  Get field list for this query expression.

  For a UNION of query blocks, return the field list generated
  during prepare.
  For a single query block, return the field list after all possible
  intermediate query processing steps are completed.

  @returns List containing fields of the query expression.
*/

List<Item> *st_select_lex_unit::get_field_list()
{
  if (is_union())
  {
    DBUG_ASSERT(prepared);
    /* Types are generated during prepare */
    return &types;
  }

  return first_select()->join->fields;
}


/**
  Cleanup after preparation or one round of execution.

  @return false if previous execution was successful, and true otherwise
*/

bool st_select_lex::cleanup()
{
  bool error= FALSE;
  DBUG_ENTER("st_select_lex::cleanup()");

  error= cleanup_level();
  for (SELECT_LEX_UNIT *lex_unit= first_inner_unit(); lex_unit;
       lex_unit= lex_unit->next_unit())
  {
    error|= lex_unit->cleanup();
  }

  DBUG_RETURN(error);
}


/**
  Cleanup only this select_lex after preparation or one round of
  execution.

  @return false if previous execution was successful, and true otherwise
*/
bool st_select_lex::cleanup_level()
{
  bool error= FALSE;

  if (join)
  {
    DBUG_ASSERT((st_select_lex*)join->select_lex == this);
    error= join->destroy();
    delete join;
    join= 0;
  }

  cur_pos_in_all_fields= ALL_FIELDS_UNDEF_POS;
  non_agg_fields.empty();
  inner_refs_list.empty();

  return error;
}


void st_select_lex::cleanup_all_joins(bool full)
{
  SELECT_LEX_UNIT *unit;
  SELECT_LEX *sl;

  if (join)
    join->cleanup(full);

  for (unit= first_inner_unit(); unit; unit= unit->next_unit())
    for (sl= unit->first_select(); sl; sl= sl->next_select())
      sl->cleanup_all_joins(full);
}