/* Copyright (c) 2000, 2017, Oracle and/or its affiliates.
   Copyright (c) 2010, 2020, MariaDB Corporation.

   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, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1335  USA */


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

#include "mariadb.h"
#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_view.h"
#include "sql_cte.h"

bool mysql_union(THD *thd, LEX *lex, select_result *result,
                 SELECT_LEX_UNIT *unit, ulong setup_tables_done_option)
{
  DBUG_ENTER("mysql_union");
  bool res;
  if (!(res= unit->prepare(unit->derived, result, SELECT_NO_UNLOCK |
                           setup_tables_done_option)))
    res= unit->exec();
  res|= unit->cleanup();
  DBUG_RETURN(res);
}


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

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

/**
  This called by SELECT_LEX_UNIT::exec when select changed
*/

void select_unit::change_select()
{
  uint current_select_number= thd->lex->current_select->select_number;
  DBUG_ENTER("select_unit::change_select");
  DBUG_PRINT("enter", ("select in unit change: %u -> %u",
                       curr_sel, current_select_number));
  DBUG_ASSERT(curr_sel != current_select_number);
  curr_sel= current_select_number;
  /* New SELECT processing starts */
  DBUG_ASSERT(table->file->inited == 0);
  step= thd->lex->current_select->linkage;
  switch (step)
  {
  case INTERSECT_TYPE:
    intersect_mark->value= prev_step= curr_step;
    curr_step= current_select_number;
    break;
  case EXCEPT_TYPE:
    break;
  default:
    step= UNION_TYPE;
    break;
  }
  DBUG_VOID_RETURN;
}
/**
  Fill temporary tables for UNION/EXCEPT/INTERSECT

  @Note
UNION:
  just add records to the table (with 'counter' field first if INTERSECT
  present in the sequence).
EXCEPT:
  looks for the record in the table (with 'counter' field first if
  INTERSECT present in the sequence) and delete it if found
INTESECT:
  looks for the same record with 'counter' field of previous operation,
  put as a 'counter' number of the current SELECT.
    We scan the table and remove all records which marked with not last
  'counter' after processing all records in send_eof and only if it last
  SELECT of sequence of INTERSECTS.

  @param values          List of record items to process.

  @retval  0 - OK
  @retval -1 - duplicate
  @retval  1 - error
*/
int select_unit::send_data(List<Item> &values)
{
  int rc;
  int not_reported_error= 0;
  if (unit->offset_limit_cnt)
  {						// using limit offset,count
    unit->offset_limit_cnt--;
    return 0;
  }
  if (thd->killed == ABORT_QUERY)
    return 0;
  if (table->no_rows_with_nulls)
    table->null_catch_flags= CHECK_ROW_FOR_NULLS_TO_REJECT;
  if (intersect_mark)
  {
    fill_record(thd, table, table->field + 1, values, TRUE, FALSE);
    table->field[0]->store((ulonglong) curr_step, 1);
  }
  else
    fill_record(thd, table, table->field, values, TRUE, FALSE);
  if (unlikely(thd->is_error()))
  {
    rc= 1;
    goto end;
  }
  if (table->no_rows_with_nulls)
  {
    table->null_catch_flags&= ~CHECK_ROW_FOR_NULLS_TO_REJECT;
    if (table->null_catch_flags)
    {
      rc= 0;
      goto end;
    }
  }

  // select_unit::change_select() change step & Co correctly for each SELECT
  switch (step)
  {
    case UNION_TYPE:
    {
      if (unlikely((write_err=
                    table->file->ha_write_tmp_row(table->record[0]))))
      {
        if (write_err == HA_ERR_FOUND_DUPP_KEY)
        {
          /*
            Inform upper level that we found a duplicate key, that should not
            be counted as part of limit
          */
          rc= -1;
          goto end;
        }
        bool is_duplicate= FALSE;
        /* create_internal_tmp_table_from_heap will generate error if needed */
        if (table->file->is_fatal_error(write_err, HA_CHECK_DUP) &&
            create_internal_tmp_table_from_heap(thd, table,
                                                tmp_table_param.start_recinfo,
                                                &tmp_table_param.recinfo,
                                                write_err, 1, &is_duplicate))
        {
          rc= 1;
          goto end;
        }

        if (is_duplicate)
        {
          rc= -1;
          goto end;
        }
      }
      break;
    }
    case EXCEPT_TYPE:
    {
      int find_res;
      /*
        The temporary table uses very first index or constrain for
        checking unique constrain.
      */
      if (!(find_res= table->file->find_unique_row(table->record[0], 0)))
      {
        DBUG_ASSERT(!table->triggers);
        table->status|= STATUS_DELETED;
        not_reported_error= table->file->ha_delete_tmp_row(table->record[0]);
        rc= MY_TEST(not_reported_error);
        goto end;
      }
      else
      {
        if ((rc= not_reported_error= (find_res != 1)))
          goto end;
      }
      break;
    }
    case INTERSECT_TYPE:
    {
      int find_res;
      /*
        The temporary table uses very first index or constrain for
        checking unique constrain.
      */
      if (!(find_res= table->file->find_unique_row(table->record[0], 0)))
      {
        DBUG_ASSERT(!table->triggers);
        if (table->field[0]->val_int() != prev_step)
        {
          rc= 0;
          goto end;
        }
        store_record(table, record[1]);
        table->field[0]->store(curr_step, 0);
        not_reported_error= table->file->ha_update_tmp_row(table->record[1],
                                                            table->record[0]);
        rc= MY_TEST(not_reported_error);
        DBUG_ASSERT(rc != HA_ERR_RECORD_IS_THE_SAME);
        goto end;
      }
      else
      {
        if ((rc= not_reported_error= (find_res != 1)))
          goto end;
      }
      break;
    }
    default:
      DBUG_ASSERT(0);
  }
  rc= 0;

end:
  if (unlikely(not_reported_error))
  {
    DBUG_ASSERT(rc);
    table->file->print_error(not_reported_error, MYF(0));
  }
  return rc;
}

bool select_unit::send_eof()
{
  if (step != INTERSECT_TYPE ||
      (thd->lex->current_select->next_select() &&
       thd->lex->current_select->next_select()->linkage == INTERSECT_TYPE))
  {
    /*
      it is not INTESECT or next SELECT in the sequence is INTERSECT so no
      need filtering (the last INTERSECT in this sequence of intersects will
      filter).
    */
    return 0;
  }

  /*
    It is last select in the sequence of INTERSECTs so we should filter out
    all records except marked with actual counter.

   TODO: as optimization for simple case this could be moved to
   'fake_select' WHERE condition
  */
  handler *file= table->file;
  int error;

  if (unlikely(file->ha_rnd_init_with_error(1)))
    return 1;

  do
  {
    if (unlikely(error= file->ha_rnd_next(table->record[0])))
    {
      if (error == HA_ERR_END_OF_FILE)
      {
        error= 0;
        break;
      }
      break;
    }
    if (table->field[0]->val_int() != curr_step)
      error= file->ha_delete_tmp_row(table->record[0]);
  } while (likely(!error));
  file->ha_rnd_end();

  if (unlikely(error))
    table->file->print_error(error, MYF(0));

  return(MY_TEST(error));
}


int select_union_recursive::send_data(List<Item> &values)
{
  int rc= select_unit::send_data(values);

  if (rc == 0 &&
      write_err != HA_ERR_FOUND_DUPP_KEY &&
      write_err != HA_ERR_FOUND_DUPP_UNIQUE)
  { 
    int err;
    if ((err= incr_table->file->ha_write_tmp_row(table->record[0])))
    {
      bool is_duplicate;
      rc= create_internal_tmp_table_from_heap(thd, incr_table,
                                              tmp_table_param.start_recinfo, 
                                              &tmp_table_param.recinfo,
					      err, 1, &is_duplicate);
    }
  }
  
  return rc;
}


bool select_unit::flush()
{
  int error;
  if (unlikely((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_unit::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
      create_table       whether to physically create result table
      keep_row_order     keep rows in order as they were inserted
      hidden             number of hidden fields (for INTERSECT)

  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_unit::create_result_table(THD *thd_arg, List<Item> *column_types,
                                  bool is_union_distinct, ulonglong options,
                                 const LEX_CSTRING *alias,
                                  bool bit_fields_as_long, bool create_table,
                                  bool keep_row_order,
                                  uint hidden)
{
  DBUG_ASSERT(table == 0);
  tmp_table_param.init();
  tmp_table_param.field_count= column_types->elements;
  tmp_table_param.bit_fields_as_long= bit_fields_as_long;
  tmp_table_param.hidden_field_count= hidden;

  if (! (table= create_tmp_table(thd_arg, &tmp_table_param, *column_types,
                                 (ORDER*) 0, is_union_distinct, 1,
                                 options, HA_POS_ERROR, alias,
                                 !create_table, keep_row_order)))
    return TRUE;

  table->keys_in_use_for_query.clear_all();
  for (uint i=0; i < table->s->fields; i++)
    table->field[i]->flags &= ~(PART_KEY_FLAG | PART_INDIRECT_KEY_FLAG);

  if (create_table)
  {
    table->file->extra(HA_EXTRA_WRITE_CACHE);
    table->file->extra(HA_EXTRA_IGNORE_DUP_KEY);
  }
  return FALSE;
}

bool
select_union_recursive::create_result_table(THD *thd_arg,
                                            List<Item> *column_types,
                                            bool is_union_distinct,
                                            ulonglong options,
                                            const LEX_CSTRING *alias,
                                            bool bit_fields_as_long,
                                            bool create_table,
                                            bool keep_row_order,
                                            uint hidden)
{
  if (select_unit::create_result_table(thd_arg, column_types,
                                       is_union_distinct, options,
                                       &empty_clex_str, bit_fields_as_long,
                                       create_table, keep_row_order,
                                       hidden))
    return true;
  
  incr_table_param.init();
  incr_table_param.field_count= column_types->elements;
  incr_table_param.bit_fields_as_long= bit_fields_as_long;
  if (! (incr_table= create_tmp_table(thd_arg, &incr_table_param, *column_types,
                                      (ORDER*) 0, false, 1,
                                      options, HA_POS_ERROR, &empty_clex_str,
                                      true, keep_row_order)))
    return true;

  incr_table->keys_in_use_for_query.clear_all();
  for (uint i=0; i < table->s->fields; i++)
    incr_table->field[i]->flags &= ~(PART_KEY_FLAG | PART_INDIRECT_KEY_FLAG);

  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_unit::cleanup()
{
  table->file->extra(HA_EXTRA_RESET_STATE);
  table->file->ha_delete_all_rows();
}


void select_union_recursive::cleanup()
{
  if (table)
  {
    select_unit::cleanup();
    free_tmp_table(thd, table);
  }

  if (incr_table)
  {
    if (incr_table->is_created())
    {
      incr_table->file->extra(HA_EXTRA_RESET_STATE);
      incr_table->file->ha_delete_all_rows();
    }
    free_tmp_table(thd, incr_table);
  }

  List_iterator<TABLE_LIST> it(rec_table_refs);
  TABLE_LIST *tbl;
  while ((tbl= it++))
  {
    TABLE *tab= tbl->table;
    if (tab->is_created())
    {
      tab->file->extra(HA_EXTRA_RESET_STATE);
      tab->file->ha_delete_all_rows();
    }
    /*
      The table will be closed later in close_thread_tables(),
      because it might be used in the statements like
      ANALYZE WITH r AS (...) SELECT * from r
      where r is defined through recursion.
    */
    tab->next= thd->rec_tables;
    thd->rec_tables= tab;
    tbl->derived_result= 0;
  }
}


/**
  Replace the current result with new_result and prepare it.  

  @param new_result New result pointer

  @retval FALSE Success
  @retval TRUE  Error
*/

bool select_union_direct::change_result(select_result *new_result)
{
  result= new_result;
  return (result->prepare(unit->types, unit) || result->prepare2(NULL));
}


bool select_union_direct::postponed_prepare(List<Item> &types)
{
  if (result != NULL)
    return (result->prepare(types, unit) || result->prepare2(NULL));
  else
    return false;
}


bool select_union_direct::send_result_set_metadata(List<Item> &list, uint flags)
{
  if (done_send_result_set_metadata)
    return false;
  done_send_result_set_metadata= true;

  /*
    Set global offset and limit to be used in send_data(). These can
    be variables in prepared statements or stored programs, so they
    must be reevaluated for each execution.
   */
  offset= unit->global_parameters()->get_offset();
  limit= unit->global_parameters()->get_limit();
  if (limit + offset >= limit)
    limit+= offset;
  else
    limit= HA_POS_ERROR; /* purecov: inspected */

  return result->send_result_set_metadata(unit->types, flags);
}


int select_union_direct::send_data(List<Item> &items)
{
  if (!limit)
    return false;
  limit--;
  if (offset)
  {
    offset--;
    return false;
  }

  send_records++;
  fill_record(thd, table, table->field, items, true, false);
  if (unlikely(thd->is_error()))
    return true; /* purecov: inspected */

  return result->send_data(unit->item_list);
}


bool select_union_direct::initialize_tables (JOIN *join)
{
  if (done_initialize_tables)
    return false;
  done_initialize_tables= true;

  return result->initialize_tables(join);
}


bool select_union_direct::send_eof()
{
  // Reset for each SELECT_LEX, so accumulate here
  limit_found_rows+= thd->limit_found_rows;

  if (unit->thd->lex->current_select == last_select_lex)
  {
    thd->limit_found_rows= limit_found_rows;

    // Reset and make ready for re-execution
    done_send_result_set_metadata= false;
    done_initialize_tables= false;

    return result->send_eof();
  }
  else
    return false;
}


/*
  initialization procedures before fake_select_lex preparation()

  SYNOPSIS
    st_select_lex_unit::init_prepare_fake_select_lex()
    thd		- thread handler
    first_execution - TRUE at the first execution of the union 

  RETURN
    options of SELECT
*/

void
st_select_lex_unit::init_prepare_fake_select_lex(THD *thd_arg,
                                                  bool first_execution) 
{
  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();
  /*
    The flag fake_select_lex->first_execution indicates whether this is
    called at the first execution of the statement, while first_execution
    shows whether this is called at the first execution of the union that
    may form just a subselect.
  */
  if ((fake_select_lex->changed_elements & TOUCHED_SEL_COND) &&
      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,
                         &fake_select_lex->context);
    (*order->item)->walk(&Item::set_fake_select_as_master_processor, 0,
                         fake_select_lex);
  }
}


bool st_select_lex_unit::prepare_join(THD *thd_arg, SELECT_LEX *sl,
                                      select_result *tmp_result,
                                      ulong additional_options,
                                      bool is_union_select)
{
  DBUG_ENTER("st_select_lex_unit::prepare_join");
  TABLE_LIST *derived= sl->master_unit()->derived;
  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);
  if (!join)
    DBUG_RETURN(true);

  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,
                             (derived && derived->merged ? NULL : sl->where),
                             (can_skip_order_by ? 0 :
                              sl->order_list.elements) +
                             sl->group_list.elements,
                             can_skip_order_by ?
                             NULL : sl->order_list.first,
                             can_skip_order_by,
                             sl->group_list.first,
                             sl->having,
                             (is_union_select ? NULL :
                              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 (unlikely(saved_error || (saved_error= thd_arg->is_fatal_error)))
    DBUG_RETURN(true);
  /*
    Remove all references from the select_lex_units to the subqueries that
    are inside the ORDER BY clause.
  */
  if (can_skip_order_by)
  {
    for (ORDER *ord= (ORDER *)sl->order_list.first; ord; ord= ord->next)
    {
      (*ord->item)->walk(&Item::eliminate_subselect_processor, FALSE, NULL);
    }
  }
  DBUG_RETURN(false);
}


/**
  Aggregate data type handlers for the "count" leftmost UNION parts.
*/
bool st_select_lex_unit::join_union_type_handlers(THD *thd_arg,
                                                  Type_holder *holders,
                                                  uint count)
{
  DBUG_ENTER("st_select_lex_unit::join_union_type_handlers");
  SELECT_LEX *first_sl= first_select(), *sl= first_sl;
  for (uint i= 0; i < count ; sl= sl->next_select(), i++)
  {
    Item *item;
    List_iterator_fast<Item> it(sl->item_list);
    for (uint pos= 0; (item= it++); pos++)
    {
      const Type_handler *item_type_handler= item->real_type_handler();
      if (sl == first_sl)
        holders[pos].set_handler(item_type_handler);
      else
      {
        DBUG_ASSERT(first_sl->item_list.elements == sl->item_list.elements);
        if (holders[pos].aggregate_for_result(item_type_handler))
        {
          my_error(ER_ILLEGAL_PARAMETER_DATA_TYPES2_FOR_OPERATION, MYF(0),
                   holders[pos].type_handler()->name().ptr(),
                   item_type_handler->name().ptr(),
                   "UNION");
          DBUG_RETURN(true);
        }
      }
    }
  }
  DBUG_RETURN(false);
}


/**
  Aggregate data type attributes for the "count" leftmost UNION parts.
*/
bool st_select_lex_unit::join_union_type_attributes(THD *thd_arg,
                                                    Type_holder *holders,
                                                    uint count)
{
  DBUG_ENTER("st_select_lex_unit::join_union_type_attributes");
  SELECT_LEX *sl, *first_sl= first_select();
  uint item_pos;
  for (uint pos= 0; pos < first_sl->item_list.elements; pos++)
  {
    if (holders[pos].alloc_arguments(thd_arg, count))
      DBUG_RETURN(true);
  }
  for (item_pos= 0, sl= first_sl ;
       item_pos < count;
       sl= sl->next_select(), item_pos++)
  {
    Item *item_tmp;
    List_iterator_fast<Item> itx(sl->item_list);
    for (uint holder_pos= 0 ; (item_tmp= itx++); holder_pos++)
    {
      /*
        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();
      holders[holder_pos].add_argument(item_tmp);
    }
  }
  for (uint pos= 0; pos < first_sl->item_list.elements; pos++)
  {
    if (holders[pos].aggregate_attributes(thd_arg))
      DBUG_RETURN(true);
  }
  DBUG_RETURN(false);
}


/**
  Join data types for the leftmost "count" UNION parts
  and store corresponding Item_type_holder's into "types".
*/
bool st_select_lex_unit::join_union_item_types(THD *thd_arg,
                                               List<Item> &types,
                                               uint count)
{
  DBUG_ENTER("st_select_lex_unit::join_union_select_list_types");
  SELECT_LEX *first_sl= first_select();
  Type_holder *holders;

  if (!(holders= new (thd_arg->mem_root)
                 Type_holder[first_sl->item_list.elements]) ||
     join_union_type_handlers(thd_arg, holders, count) ||
     join_union_type_attributes(thd_arg, holders, count))
    DBUG_RETURN(true);

  bool is_recursive= with_element && with_element->is_recursive;
  types.empty();
  List_iterator_fast<Item> it(first_sl->item_list);
  Item *item_tmp;
  for (uint pos= 0; (item_tmp= it++); pos++)
  {
    /*
      SQL standard requires forced nullability only for
      recursive columns. However type aggregation in our
      implementation so far does not differentiate between
      recursive and non-recursive columns of a recursive CTE.
      TODO: this should be fixed.
    */
    bool pos_maybe_null= is_recursive ? true : holders[pos].get_maybe_null();

    /* Error's in 'new' will be detected after loop */
    types.push_back(new (thd_arg->mem_root)
                    Item_type_holder(thd_arg,
                                     item_tmp,
                                     holders[pos].type_handler(),
                                     &holders[pos]/*Type_all_attributes*/,
                                     pos_maybe_null));
  }
  if (unlikely(thd_arg->is_fatal_error))
    DBUG_RETURN(true); // out of memory
  DBUG_RETURN(false);
}


bool st_select_lex_unit::prepare(TABLE_LIST *derived_arg,
                                 select_result *sel_result,
                                 ulong additional_options)
{
  SELECT_LEX *lex_select_save= thd->lex->current_select;
  SELECT_LEX *sl, *first_sl= first_select();
  bool is_recursive= with_element && with_element->is_recursive;
  bool is_rec_result_table_created= false;
  uint union_part_count= 0;
  select_result *tmp_result;
  bool is_union_select;
  bool have_except= FALSE, have_intersect= FALSE;
  bool instantiate_tmp_table= false;
  bool single_tvc= !first_sl->next_select() && first_sl->tvc &&
                   !fake_select_lex;
  DBUG_ENTER("st_select_lex_unit::prepare");
  DBUG_ASSERT(thd == current_thd);

  if (is_recursive && (sl= first_sl->next_select()))
  {
    SELECT_LEX *next_sl;
    for ( ; ; sl= next_sl)
    {
      next_sl= sl->next_select();
      if (!next_sl)
        break;
      if (next_sl->with_all_modifier != sl->with_all_modifier)
      {
        my_error(ER_NOT_SUPPORTED_YET, MYF(0),
         "mix of ALL and DISTINCT UNION operations in recursive CTE spec");
        DBUG_RETURN(TRUE);
      }
    }
  }

  describe= additional_options & SELECT_DESCRIBE;

  /*
    Save fake_select_lex in case we don't need it for anything but
    global parameters.
  */
  if (saved_fake_select_lex == NULL) // Don't overwrite on PS second prepare
    saved_fake_select_lex= fake_select_lex;

  /*
    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())
      {
	if (sl->tvc)
	{
	  sl->tvc->result= result;
	  if (result->prepare(sl->item_list, this))
	    DBUG_RETURN(TRUE);
	  sl->tvc->select_options|= SELECT_DESCRIBE;
	}
	else
	{
	  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(TRUE);
	  }
	  sl->join->select_options|= SELECT_DESCRIBE;
	  sl->join->reinit();
	}
      }
    }
    DBUG_RETURN(FALSE);
  }
  prepared= 1;
  saved_error= FALSE;
  
  thd->lex->current_select= sl= first_sl;
  found_rows_for_union= first_sl->options & OPTION_FOUND_ROWS;
  is_union_select= is_unit_op() || fake_select_lex || single_tvc;

  /*
    If we are reading UNION output and the UNION is in the
    IN/ANY/ALL/EXISTS subquery, then ORDER BY is redundant and hence should
    be removed.
    Example:
     select ... col IN (select col2 FROM t1 union select col3 from t2 ORDER BY 1)

    (as for ORDER BY ... LIMIT, it currently not supported inside
     IN/ALL/ANY subqueries)
    (For non-UNION this removal of ORDER BY clause is done in
     check_and_do_in_subquery_rewrites())
  */
  if (item && is_unit_op() &&
      (item->is_in_predicate() || item->is_exists_predicate()))
  {
    global_parameters()->order_list.first= NULL;
    global_parameters()->order_list.elements= 0;
  }

  for (SELECT_LEX *s= first_sl; s; s= s->next_select())
  {
    switch (s->linkage)
    {
    case INTERSECT_TYPE:
      have_intersect= TRUE;
      break;
    case EXCEPT_TYPE:
      have_except= TRUE;
      break;
    default:
      break;
    }
  }

  /* Global option */

  if (is_union_select || is_recursive)
  {
    if ((is_unit_op() && !union_needs_tmp_table() &&
        !have_except && !have_intersect) || single_tvc)
    {
      SELECT_LEX *last= first_select();
      while (last->next_select())
        last= last->next_select();
      if (!(tmp_result= union_result=
              new (thd->mem_root) select_union_direct(thd, sel_result,
                                                          last)))
        goto err; /* purecov: inspected */
      fake_select_lex= NULL;
      instantiate_tmp_table= false;
    }
    else
    {
      if (!is_recursive)
	union_result= new (thd->mem_root) select_unit(thd);
      else
      {
        with_element->rec_result=
          new (thd->mem_root) select_union_recursive(thd);
        union_result=  with_element->rec_result;
        if (fake_select_lex)
	{
          if (fake_select_lex->order_list.first ||
              fake_select_lex->explicit_limit)
          {
	    my_error(ER_NOT_SUPPORTED_YET, MYF(0),
                     "global ORDER_BY/LIMIT in recursive CTE spec");
	    goto err;
          }
          fake_select_lex->cleanup();
          fake_select_lex= NULL;
        }
      }
      if (!(tmp_result= union_result))
        goto err; /* purecov: inspected */
      instantiate_tmp_table= true;
    }
  }
  else
    tmp_result= sel_result;

  sl->context.resolve_in_select_list= TRUE;

  if (!is_union_select && !is_recursive)
  {
    if (sl->tvc)
    {
      if (sl->tvc->prepare(thd, sl, tmp_result, this))
	goto err;
    }
    else
    {
      if (prepare_join(thd, first_sl, tmp_result, additional_options,
                     is_union_select))
        goto err;

      if (derived_arg && derived_arg->table &&
          derived_arg->derived_type == VIEW_ALGORITHM_MERGE &&
          derived_arg->table->versioned())
      {
        /* Got versioning conditions (see vers_setup_conds()), need to update
           derived_arg. */
        derived_arg->where= first_sl->where;
      }
    }
    types= first_sl->item_list;
    goto cont;
  }
 
  for (;sl; sl= sl->next_select(), union_part_count++)
  {
    if (sl->tvc)
    {
      if (sl->tvc->to_be_wrapped_as_with_tail() &&
          !(thd->lex->context_analysis_only & CONTEXT_ANALYSIS_ONLY_VIEW))

      {
        st_select_lex *wrapper_sl= wrap_tvc_with_tail(thd, sl);
        if (!wrapper_sl)
          goto err;

        if (sl == first_sl)
          first_sl= wrapper_sl;
        sl= wrapper_sl;

        if (prepare_join(thd, sl, tmp_result, additional_options,
                         is_union_select))
	  goto err;
      }
      else if (sl->tvc->prepare(thd, sl, tmp_result, this))
	goto err;
    }
    else if (prepare_join(thd, sl, tmp_result, additional_options,
                          is_union_select))
      goto err;

    /*
      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;

    /*
      Use items list of underlaid select for derived tables to preserve
      information about fields lengths and exact types
    */
    if (sl == first_sl)
    {
      if (with_element)
      {
        if (with_element->rename_columns_of_derived_unit(thd, this))
          goto err;
        if (check_duplicate_names(thd, sl->item_list, 0))
          goto err;
      }
    }
    else
    {
      if (first_sl->item_list.elements != sl->item_list.elements)
      {
        my_message(ER_WRONG_NUMBER_OF_COLUMNS_IN_SELECT,
                   ER_THD(thd, ER_WRONG_NUMBER_OF_COLUMNS_IN_SELECT),
                   MYF(0));
        goto err;
      }
    }
    if (is_recursive)
    {
      if (!with_element->is_anchor(sl))
        sl->uncacheable|= UNCACHEABLE_UNITED;
      if (!is_rec_result_table_created &&
          (!sl->next_select() ||
           sl->next_select() == with_element->first_recursive))
      {
        ulonglong create_options;
        create_options= (first_sl->options | thd->variables.option_bits |
                         TMP_TABLE_ALL_COLUMNS);
        // Join data types for all non-recursive parts of a recursive UNION
        if (join_union_item_types(thd, types, union_part_count + 1))
          goto err;
        if (union_result->create_result_table(thd, &types,
                                              MY_TEST(union_distinct),
                                              create_options,
                                              &derived_arg->alias, false,
                                              instantiate_tmp_table, false,
                                              0))
          goto err;
        if (!derived_arg->table)
        {
          bool res= false;

          if ((!derived_arg->is_with_table_recursive_reference() ||
               !derived_arg->derived_result) &&
              !(derived_arg->derived_result=
                new (thd->mem_root) select_unit(thd)))
            goto err; // out of memory
          thd->create_tmp_table_for_derived= TRUE;

          res= derived_arg->derived_result->create_result_table(thd,
                                                            &types,
                                                            FALSE,
                                                            create_options,
                                                            &derived_arg->alias,
                                                            FALSE, FALSE,
                                                            FALSE, 0);
          thd->create_tmp_table_for_derived= FALSE;
          if (res)
            goto err;
          derived_arg->derived_result->set_unit(this);
          derived_arg->table= derived_arg->derived_result->table;
          if (derived_arg->is_with_table_recursive_reference())
          {
            /* Here 'derived_arg' is the primary recursive table reference */
            derived_arg->with->rec_result->
              rec_table_refs.push_back(derived_arg);
          }
        }
        with_element->mark_as_with_prepared_anchor();
        is_rec_result_table_created= true;
      }
    }      
  }
  // In case of a non-recursive UNION, join data types for all UNION parts.
  if (!is_recursive && join_union_item_types(thd, types, union_part_count))
    goto err;

cont:
  /*
    If the query is using select_union_direct, we have postponed
    preparation of the underlying select_result until column types
    are known.
  */
  if (union_result != NULL && union_result->postponed_prepare(types))
    DBUG_RETURN(true);

  if (is_union_select)
  {
    /*
      Check that it was possible to aggregate
      all collations together for UNION.
    */
    List_iterator_fast<Item> tp(types);
    Item *type;
    ulonglong create_options;
    uint save_tablenr= 0;
    table_map save_map= 0;
    uint save_maybe_null= 0;

    while ((type= tp++))
    {
      if (type->cmp_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, &ft))
        {
          my_error (ER_CANT_USE_OPTION_HERE, MYF(0), "MATCH()");
          goto err;
        }
    }


    create_options= (first_sl->options | thd->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 (!is_recursive)
    {
      uint hidden= 0;
      if (have_intersect)
      {
        hidden= 1;
        if (!intersect_mark)
        {
          /*
            For intersect we add a hidden column first that contains
            the current select number of the time when the row was
            added to the temporary table
          */

          Query_arena *arena, backup_arena;
          arena= thd->activate_stmt_arena_if_needed(&backup_arena);

          intersect_mark= new (thd->mem_root) Item_int(thd, 0);

          if (arena)
            thd->restore_active_arena(arena, &backup_arena);

          if (!intersect_mark)
            goto err;
        }
        else
          intersect_mark->value= 0; //reset
        types.push_front(union_result->intersect_mark= intersect_mark);
        union_result->intersect_mark->name.str= "___";
        union_result->intersect_mark->name.length= 3;
      }
      bool error=
        union_result->create_result_table(thd, &types,
                                          MY_TEST(union_distinct),
                                          create_options, &empty_clex_str, false,
                                          instantiate_tmp_table, false,
                                          hidden);
      if (intersect_mark)
        types.pop();
      if (unlikely(error))
        goto err;
    }
    if (fake_select_lex && !fake_select_lex->first_cond_optimization)
    {
      save_tablenr= result_table_list.tablenr_exec;
      save_map= result_table_list.map_exec;
      save_maybe_null= result_table_list.maybe_null_exec;
    }
    bzero((char*) &result_table_list, sizeof(result_table_list));
    result_table_list.db.str= (char*) "";
    result_table_list.db.length= 0;
    result_table_list.table_name.str= result_table_list.alias.str= "union";
    result_table_list.table_name.length= result_table_list.alias.length= sizeof("union")-1;
    result_table_list.table= table= union_result->table;
    if (fake_select_lex && !fake_select_lex->first_cond_optimization)
    {
      result_table_list.tablenr_exec= save_tablenr;
      result_table_list.map_exec= save_map;
      result_table_list.maybe_null_exec= save_maybe_null;
    }

    thd->lex->current_select= lex_select_save;
    if (!item_list.elements)
    {
      Query_arena *arena, backup_arena;

      arena= thd->activate_stmt_arena_if_needed(&backup_arena);
      
      saved_error= table->fill_item_list(&item_list);
      // Item_list is inherited from 'types', so there could be the counter
      if (intersect_mark)
        item_list.pop(); // remove intersect counter

      if (arena)
        thd->restore_active_arena(arena, &backup_arena);

      if (unlikely(saved_error))
        goto err;

      if (fake_select_lex != NULL &&
          (thd->stmt_arena->is_stmt_prepare() ||
           (thd->lex->context_analysis_only & CONTEXT_ANALYSIS_ONLY_VIEW)))
      {
        /* Validate the global parameters of this union */

	init_prepare_fake_select_lex(thd, TRUE);
        /* Should be done only once (the only item_list per statement) */
        DBUG_ASSERT(fake_select_lex->join == 0);
	if (!(fake_select_lex->join= new JOIN(thd, item_list, thd->variables.option_bits,
					      result)))
	{
	  fake_select_lex->table_list.empty();
	  DBUG_RETURN(TRUE);
	}

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

	thd->lex->current_select= fake_select_lex;

        /*
          We need to add up n_sum_items in order to make the correct
          allocation in setup_ref_array().
        */
        fake_select_lex->n_child_sum_items+= global_parameters()->n_sum_items;
      }
    }
    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, intersect_mark ? 1 : 0);
    }
    if (fake_select_lex != NULL &&
        (thd->stmt_arena->is_stmt_prepare() ||
         (thd->lex->context_analysis_only & CONTEXT_ANALYSIS_ONLY_VIEW)))
    {
      if (!fake_select_lex->join &&
          !(fake_select_lex->join=
            new JOIN(thd, item_list, thd->variables.option_bits, result)))
      {
         fake_select_lex->table_list.empty();
         DBUG_RETURN(TRUE);
      }
      saved_error= fake_select_lex->join->
        prepare(fake_select_lex->table_list.first, 0, 0,
                global_parameters()->order_list.elements, // og_num
                global_parameters()->order_list.first,    // order
                false, NULL, NULL, NULL, fake_select_lex, this);
      fake_select_lex->table_list.empty();
    }
  }

  thd->lex->current_select= lex_select_save;

  DBUG_RETURN(saved_error || thd->is_fatal_error);

err:
  thd->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()
{
  SELECT_LEX *lex_select_save= thd->lex->current_select;
  SELECT_LEX *select_cursor=first_select();
  DBUG_ENTER("st_select_lex_unit::optimize");

  if (optimized && !uncacheable && !describe)
    DBUG_RETURN(FALSE);

  if (with_element && with_element->is_recursive && optimize_started)
    DBUG_RETURN(FALSE);
  optimize_started= true;

  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();
      }
      if (table->is_created())
      {
        table->file->ha_delete_all_rows();
        table->file->info(HA_STATUS_VARIABLE);
      }
      /* 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= select_cursor; sl; sl= sl->next_select())
    {
      if (sl->tvc)
      {
	sl->tvc->select_options=
          (select_limit_cnt == HA_POS_ERROR || sl->braces) ?
          sl->options & ~OPTION_FOUND_ROWS : sl->options | found_rows_for_union;
	if (sl->tvc->optimize(thd))
        {
          thd->lex->current_select= lex_select_save;
          DBUG_RETURN(TRUE);
        }
        if (derived)
	  sl->increase_derived_records(sl->tvc->get_records());
	continue;
      }
      thd->lex->current_select= sl;

      if (optimized)
	saved_error= sl->join->reinit();
      else
      {
        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;
        }

        /*
          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();
      }

      if (unlikely(saved_error))
      {
	thd->lex->current_select= lex_select_save;
	DBUG_RETURN(saved_error);
      }
    }
  }
  optimized= 1;

  thd->lex->current_select= lex_select_save;
  DBUG_RETURN(saved_error);
}


bool st_select_lex_unit::exec()
{
  SELECT_LEX *lex_select_save= thd->lex->current_select;
  SELECT_LEX *select_cursor=first_select();
  ulonglong add_rows=0;
  ha_rows examined_rows= 0;
  bool first_execution= !executed;
  DBUG_ENTER("st_select_lex_unit::exec");
  bool was_executed= executed;

  if (executed && !uncacheable && !describe)
    DBUG_RETURN(FALSE);
  executed= 1;
  if (!(uncacheable & ~UNCACHEABLE_EXPLAIN) && item &&
      !item->with_recursive_reference)
    item->make_const();
  
  saved_error= optimize();
  
  create_explain_query_if_not_exists(thd->lex, thd->mem_root);

  if (!saved_error && !was_executed)
    save_union_explain(thd->lex->explain);

  if (unlikely(saved_error))
    DBUG_RETURN(saved_error);

  if (union_result)
  {
    union_result->init();
    if (uncacheable & UNCACHEABLE_DEPENDENT &&
        union_result->table && union_result->table->is_created())
    {
      union_result->table->file->ha_delete_all_rows();
      union_result->table->file->ha_enable_indexes(HA_KEY_SWITCH_ALL);
    }
  }

  if (uncacheable || !item || !item->assigned() || describe)
  {
    if (!fake_select_lex && !(with_element && with_element->is_recursive))
      union_result->cleanup();
    for (SELECT_LEX *sl= select_cursor; sl; sl= sl->next_select())
    {
      ha_rows records_at_start= 0;
      thd->lex->current_select= sl;
      if (union_result)
        union_result->change_select();
      if (fake_select_lex)
      {
        if (sl != &thd->lex->select_lex)
          fake_select_lex->uncacheable|= sl->uncacheable;
        else
          fake_select_lex->uncacheable= 0;
      }

      {
        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;
        }

        /*
          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.
        */
	if (sl->tvc)
	{
	  sl->tvc->select_options=
             (select_limit_cnt == HA_POS_ERROR || sl->braces) ?
             sl->options & ~OPTION_FOUND_ROWS : sl->options | found_rows_for_union;
	  saved_error= sl->tvc->optimize(thd);
	}
	else
	{
          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();
	}
      }
      if (likely(!saved_error))
      {
	records_at_start= table->file->stats.records;
	if (sl->tvc)
	  sl->tvc->exec(sl);
	else
	  sl->join->exec();
        if (sl == union_distinct && !(with_element && with_element->is_recursive))
	{
          // This is UNION DISTINCT, so there should be a fake_select_lex
          DBUG_ASSERT(fake_select_lex != NULL);
	  if (unlikely(table->file->ha_disable_indexes(HA_KEY_SWITCH_ALL)))
	    DBUG_RETURN(TRUE);
	  table->no_keyread=1;
	}
	if (!sl->tvc)
	  saved_error= sl->join->error;
	offset_limit_cnt= (ha_rows)(sl->offset_limit ?
                                    sl->offset_limit->val_uint() :
                                    0);
	if (likely(!saved_error))
	{
	  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(1);
	  }
	}
      }
      if (unlikely(saved_error))
      {
	thd->lex->current_select= lex_select_save;
	DBUG_RETURN(saved_error);
      }
      if (fake_select_lex != NULL)
      {
        /* Needed for the following test and for records_at_start in next loop */
        int error= table->file->info(HA_STATUS_VARIABLE);
        if (unlikely(error))
        {
          table->file->print_error(error, MYF(0));
          DBUG_RETURN(1);
        }
      }
      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 (thd->killed == ABORT_QUERY)
      {
        /*
          Stop execution of the remaining queries in the UNIONS, and produce
          the current result.
        */
        push_warning_printf(thd, Sql_condition::WARN_LEVEL_WARN,
                            ER_QUERY_EXCEEDED_ROWS_EXAMINED_LIMIT,
                            ER_THD(thd, ER_QUERY_EXCEEDED_ROWS_EXAMINED_LIMIT),
                            thd->accessed_rows_and_keys,
                            thd->lex->limit_rows_examined->val_uint());
        thd->reset_killed();
        break;
      }
    }
  }

  DBUG_EXECUTE_IF("show_explain_probe_union_read", 
                   dbug_serve_apcs(thd, 1););
  {
    List<Item_func_match> empty_list;
    empty_list.empty();
    /*
      Disable LIMIT ROWS EXAMINED in order to produce the possibly incomplete
      result of the UNION without interruption due to exceeding the limit.
    */
    thd->lex->limit_rows_examined_cnt= ULONGLONG_MAX;

    // Check if EOM
    if (fake_select_lex != NULL && likely(!thd->is_fatal_error))
    {
       /* Send result to 'result' */
       saved_error= true;

      set_limit(global_parameters());
      init_prepare_fake_select_lex(thd, first_execution);
      JOIN *join= fake_select_lex->join;
      saved_error= false;
      if (!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 (unlikely(!(fake_select_lex->join=
                       new JOIN(thd, item_list, fake_select_lex->options,
                                result))))
	{
	  fake_select_lex->table_list.empty();
	  goto err;
	}
        fake_select_lex->join->no_const_tables= TRUE;

        /*
          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;
        
        if (!was_executed)
          save_union_explain_part2(thd->lex->explain);

        saved_error= mysql_select(thd,
                              &result_table_list,
                              0, item_list, NULL,
				  global_parameters()->order_list.elements,
				  global_parameters()->order_list.first,
                              NULL, NULL, NULL,
                              fake_select_lex->options | SELECT_NO_UNLOCK,
                              result, this, fake_select_lex);
      }
      else
      {
        if (describe)
        {
          /*
            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):
          */ // psergey-todo: is the above really necessary anymore?? 
	  join->init(thd, item_list, fake_select_lex->options, result);
          saved_error= mysql_select(thd,
                                &result_table_list,
                                0, item_list, NULL,
				    global_parameters()->order_list.elements,
				    global_parameters()->order_list.first,
                                NULL, NULL, NULL,
                                fake_select_lex->options | SELECT_NO_UNLOCK,
                                result, this, fake_select_lex);
        }
        else
        {
          join->join_examined_rows= 0;
          saved_error= join->reinit();
          join->exec();
        }
      }

      fake_select_lex->table_list.empty();
      if (likely(!saved_error))
      {
	thd->limit_found_rows = (ulonglong)table->file->stats.records + add_rows;
        thd->inc_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;
err:
  thd->lex->set_limit_rows_examined();
  DBUG_RETURN(saved_error);
}


/**
  @brief
    Execute the union of the specification of a recursive with table 

  @details
    The method is performed only for the units that are specifications
    if recursive with table T. If the specification contains an anchor
    part then the first call of this method executes only this part
    while the following calls execute the recursive part. If there are
    no anchors each call executes the whole unit.
    Before the excution the method cleans up the temporary table 
    to where the new rows of the recursive table are sent.
    After the execution the unit these rows are copied to the 
    temporary tables created for recursive references of T. 
    If the specification if T is restricted (standards compliant)
    then these temporary tables are cleaned up before new rows
    are copied into them.  

  @retval
    false   on success
    true    on failure
*/

bool st_select_lex_unit::exec_recursive()
{
  st_select_lex *lex_select_save= thd->lex->current_select;
  st_select_lex *start= with_element->first_recursive;
  TABLE *incr_table= with_element->rec_result->incr_table;
  st_select_lex *end= NULL;
  bool is_unrestricted= with_element->is_unrestricted();
  List_iterator_fast<TABLE_LIST> li(with_element->rec_result->rec_table_refs);
  TMP_TABLE_PARAM *tmp_table_param= &with_element->rec_result->tmp_table_param;
  ha_rows examined_rows= 0;
  bool was_executed= executed;
  TABLE_LIST *rec_tbl;

  DBUG_ENTER("st_select_lex_unit::exec_recursive");

  executed= 1;
  create_explain_query_if_not_exists(thd->lex, thd->mem_root);
  if (!was_executed)
    save_union_explain(thd->lex->explain);

  if (with_element->level == 0)
  {
    if (!incr_table->is_created() &&
        instantiate_tmp_table(incr_table,
                              tmp_table_param->keyinfo,
                              tmp_table_param->start_recinfo,
                              &tmp_table_param->recinfo,
                              0))
      DBUG_RETURN(1);
    incr_table->file->extra(HA_EXTRA_WRITE_CACHE);
    incr_table->file->extra(HA_EXTRA_IGNORE_DUP_KEY);
    start= first_select();
    if (with_element->with_anchor)
      end= with_element->first_recursive;
  }
  else if (unlikely((saved_error= incr_table->file->ha_delete_all_rows())))
    goto err;

  for (st_select_lex *sl= start ; sl != end; sl= sl->next_select())
  {
    if (with_element->level)
    {
      for (TABLE_LIST *derived= with_element->derived_with_rec_ref.first;
           derived;
           derived= derived->next_with_rec_ref)
      {
        if (derived->is_materialized_derived())
	{
          if (derived->table->is_created())
            derived->table->file->ha_delete_all_rows();
          derived->table->reginfo.join_tab->preread_init_done= false;
        }
      }
    }
    thd->lex->current_select= sl;
    set_limit(sl);
    if (sl->tvc)
      sl->tvc->exec(sl);
    else
    {
      sl->join->exec();
      saved_error= sl->join->error;
    }
    if (likely(!saved_error))
    {
       examined_rows+= thd->get_examined_row_count();
       thd->set_examined_row_count(0);
       if (unlikely(union_result->flush()))
       {
	 thd->lex->current_select= lex_select_save;
	 DBUG_RETURN(1);
       }
    }
    if (unlikely(saved_error))
    {
      thd->lex->current_select= lex_select_save;
      goto err;
      
    }
  }

  thd->inc_examined_row_count(examined_rows);

  incr_table->file->info(HA_STATUS_VARIABLE);
  if (with_element->level && incr_table->file->stats.records == 0)
    with_element->set_as_stabilized();
  else
    with_element->level++;

  while ((rec_tbl= li++))
  {
    TABLE *rec_table= rec_tbl->table;
    saved_error=
      incr_table->insert_all_rows_into_tmp_table(thd, rec_table,
                                                 tmp_table_param,
                                                 !is_unrestricted);
    if (!with_element->rec_result->first_rec_table_to_update)
      with_element->rec_result->first_rec_table_to_update= rec_table;
    if (with_element->level == 1 && rec_table->reginfo.join_tab)
      rec_table->reginfo.join_tab->preread_init_done= true;
  }
  for (Item_subselect *sq= with_element->sq_with_rec_ref.first;
       sq;
       sq= sq->next_with_rec_ref)
  {
    sq->reset();
    sq->engine->force_reexecution();
  }   

  thd->lex->current_select= lex_select_save;
err:
  thd->lex->set_limit_rows_examined();
  DBUG_RETURN(saved_error);    
}


bool st_select_lex_unit::cleanup()
{
  bool error= 0;
  DBUG_ENTER("st_select_lex_unit::cleanup");

  if (cleaned)
  {
    DBUG_RETURN(FALSE);
  }
  if (with_element && with_element->is_recursive && union_result)
  {
    select_union_recursive *result= with_element->rec_result;
    if (++result->cleanup_count == with_element->rec_outer_references)
    {
      /*
        Perform cleanup for with_element and for all with elements
        mutually recursive with it.
      */
      cleaned= 1;
      with_element->get_next_mutually_recursive()->spec->cleanup();
    }
    else
    {
      /*
        Just increment by 1 cleanup_count for with_element and
        for all with elements mutually recursive with it.
      */
      With_element *with_elem= with_element;
      while ((with_elem= with_elem->get_next_mutually_recursive()) !=
             with_element)
        with_elem->rec_result->cleanup_count++;
      DBUG_RETURN(FALSE);
    }
  }
  columns_are_renamed= false;
  cleaned= 1;

  for (SELECT_LEX *sl= first_select(); sl; sl= sl->next_select())
    error|= sl->cleanup();
     
  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 (with_element && with_element->is_recursive)
  {
    if (union_result)
    {
      ((select_union_recursive *) union_result)->cleanup();
      delete union_result;
      union_result= 0;
    }
    with_element->mark_as_cleaned();
  }
  else
  {
    if (union_result)
    {
      delete union_result;
      union_result=0; // Safety
      if (table)
        free_tmp_table(thd, table);
      table= 0; // Safety
    }
  }

  DBUG_RETURN(error);
}


void st_select_lex_unit::reinit_exec_mechanism()
{
  prepared= optimized= optimized_2= executed= 0;
  optimize_started= 0;
  if (with_element && with_element->is_recursive)
    with_element->reset_recursive_for_exec();
}


/**
  Change the select_result object used to return the final result of
  the unit, replacing occurences of old_result with new_result.

  @param new_result New select_result object
  @param old_result Old select_result object

  @retval false Success
  @retval true  Error
*/

bool st_select_lex_unit::change_result(select_result_interceptor *new_result,
                                       select_result_interceptor *old_result)
{
  for (SELECT_LEX *sl= first_select(); sl; sl= sl->next_select())
  {
    if (sl->join)
      if (sl->join->change_result(new_result, old_result))
	return true; /* purecov: inspected */
  }
  /*
    If there were a fake_select_lex->join, we would have to change the
    result of that also, but change_result() is called before such an
    object is created.
  */
  DBUG_ASSERT(fake_select_lex == NULL || fake_select_lex->join == NULL);
  return false;
}

/*
  Get column type information for this unit.

  SYNOPSIS
    st_select_lex_unit::get_column_types()
      @param for_cursor if true return the list the fields
                        retrieved by the cursor

  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_column_types(bool for_cursor)
{
  SELECT_LEX *sl= first_select();
  bool is_procedure= !sl->tvc && sl->join->procedure ;

  if (is_procedure)
  {
    /* Types for "SELECT * FROM t1 procedure analyse()"
       are generated during execute */
    return &sl->join->procedure_fields_list;
  }


  if (is_unit_op())
  {
    DBUG_ASSERT(prepared);
    /* Types are generated during prepare */
    return &types;
  }

  return for_cursor ? sl->join->fields :  &sl->item_list;
}


static void cleanup_order(ORDER *order)
{
  for (; order; order= order->next)
    order->counter_used= 0;
}


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

  cleanup_order(order_list.first);
  cleanup_order(group_list.first);
  cleanup_ftfuncs(this);

  if (join)
  {
    List_iterator<TABLE_LIST> ti(leaf_tables);
    TABLE_LIST *tbl;
    while ((tbl= ti++))
    {
      if (tbl->is_recursive_with_table() &&
          !tbl->is_with_table_recursive_reference())
      {
        /*
          If query is killed before open_and_process_table() for tbl
          is called then 'with' is already set, but 'derived' is not.
        */
        st_select_lex_unit *unit= tbl->with->spec;
        error|= (bool) error | (uint) unit->cleanup();
      }
    }
    DBUG_ASSERT((st_select_lex*)join->select_lex == this);
    error= join->destroy();
    delete join;
    join= 0;
  }
  leaf_tables.empty();
  for (SELECT_LEX_UNIT *lex_unit= first_inner_unit(); lex_unit ;
       lex_unit= lex_unit->next_unit())
  {
    if (lex_unit->with_element && lex_unit->with_element->is_recursive)
      continue;
    error= (bool) ((uint) error | (uint) lex_unit->cleanup());
  }
  inner_refs_list.empty();
  exclude_from_table_unique_test= FALSE;
  hidden_bit_fields= 0;
  DBUG_RETURN(error);
}


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

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

  for (unit= first_inner_unit(); unit; unit= unit->next_unit())
  {
    if (unit->with_element && unit->with_element->is_recursive)
      continue;
    for (sl= unit->first_select(); sl; sl= sl->next_select())
      sl->cleanup_all_joins(full);
  }
  DBUG_VOID_RETURN;
}


/**
  Set exclude_from_table_unique_test for selects of this unit and all
  underlying selects.

  @note used to exclude materialized derived tables (views) from unique
  table check.
*/

void st_select_lex_unit::set_unique_exclude()
{
  for (SELECT_LEX *sl= first_select(); sl; sl= sl->next_select())
  {
    sl->exclude_from_table_unique_test= TRUE;
    for (SELECT_LEX_UNIT *unit= sl->first_inner_unit();
         unit;
         unit= unit->next_unit())
    {
      unit->set_unique_exclude();
    }
  }
}

/**
  @brief
  Check if the derived table is guaranteed to have distinct rows because of
  UNION operations used to populate it.

  @detail
    UNION operation removes duplicate rows from its output. That is, a query like

      select * from t1 UNION select * from t2

    will not produce duplicate rows in its output, even if table t1 (and/or t2)
    contain duplicate rows. EXCEPT and INTERSECT operations also have this
    property.

    On the other hand, UNION ALL operation doesn't remove duplicates. (The SQL
    standard also defines EXCEPT ALL and INTERSECT ALL, but we don't support
    them).

    st_select_lex_unit computes its value left to right. That is, if there is
     a st_select_lex_unit object describing

      (select #1) OP1 (select #2) OP2 (select #3)

    then ((select #1) OP1 (select #2)) is computed first, and OP2 is computed
    second.

    How can one tell if st_select_lex_unit is guaranteed to have distinct
    output rows? This depends on whether the last operation was duplicate-
    removing or not:
    - UNION ALL is not duplicate-removing
    - all other operations are duplicate-removing
*/

bool st_select_lex_unit::check_distinct_in_union()
{
  if (union_distinct && !union_distinct->next_select())
    return true;
  return false;
}
