Impressum sql_union.cc   Sprache: C

/* 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"
#include "item_windowfunc.h"

select_handler *find_partial_select_handler(THD *thd, SELECT_LEX *select_lex,
                                            SELECT_LEX_UNIT *lex_unit);

bool mysql_union(THD *thd, LEX *lex, select_result *result,
                 SELECT_LEX_UNIT *unit, ulonglong 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->get_linkage();
  switch (step)
  {
  case INTERSECT_TYPE:
    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
INTERSECT:
  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= 0;
  int not_reported_error= 0;

  if (table->no_rows_with_nulls)
    table->null_catch_flags= CHECK_ROW_FOR_NULLS_TO_REJECT;

  fill_record(thd, table, table->field + addon_cnt, values, true, false, true);
  /* set up initial values for records to be written */
  if (addon_cnt && step == UNION_TYPE)
  {
    DBUG_ASSERT(addon_cnt == 1);
    table->field[0]->store((ulonglong) curr_step, 1);
  }

  if (unlikely(thd->is_error()))
  {
    rc= 1;
    if (unlikely(not_reported_error))
    {
      DBUG_ASSERT(rc);
      table->file->print_error(not_reported_error, MYF(0));
    }
    return rc;
  }
  if (table->no_rows_with_nulls)
  {
    table->null_catch_flags&= ~CHECK_ROW_FOR_NULLS_TO_REJECT;
    if (table->null_catch_flags)
    {
      rc= 0;
      if (unlikely(not_reported_error))
      {
        DBUG_ASSERT(rc);
        table->file->print_error(not_reported_error, MYF(0));
      }
      return rc;
    }
  }

  /* select_unit::change_select() change step & Co correctly for each SELECT */
  int find_res;
  switch (step)
  {
  case UNION_TYPE:
    /* Errors not related to duplicate key are reported by write_record() */
    rc= write_record();
    /* no reaction with conversion. rc == -1 (dupp key) is ignored by caller */
    if (rc == -2)
      rc= 0;
    break;

  case EXCEPT_TYPE:
    /*
      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)))
      rc= delete_record();
    else
      rc= not_reported_error= (find_res != 1);
    break;
  case INTERSECT_TYPE:
    /*
      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)
      {
        not_reported_error= update_counter(table->field[0], curr_step);
        rc= MY_TEST(not_reported_error);
        DBUG_ASSERT(rc != HA_ERR_RECORD_IS_THE_SAME);
      }
    }
    else
      rc= not_reported_error= (find_res != 1);
    break;
  default:
    DBUG_ASSERT(0);
  }

  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()->get_linkage() == INTERSECT_TYPE))
  {
    /*
      it is not INTERSECT 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
  */
  int error;

  if (table->file->ha_rnd_init_with_error(1))
    return 1;
  do
  {
    error= table->file->ha_rnd_next(table->record[0]);
    if (unlikely(error))
    {
      if (error == HA_ERR_END_OF_FILE)
      {
        error= 0;
        break;
      }
      break;
    }
    if (table->field[0]->val_int() != curr_step)
      error= delete_record();
  } while (!error);
  table->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;
  bool save_abort_on_warning= thd->abort_on_warning;
  enum_check_fields save_count_cuted_fields= thd->count_cuted_fields;
  long save_counter;

  /*
    For recursive CTE's give warnings for wrong field info
    However, we don't do that for CREATE TABLE ... SELECT or INSERT ... SELECT
    as the upper level code for these handles setting of abort_on_warning
    depending on if 'IGNORE' is used.
  */
  if (thd->lex->sql_command != SQLCOM_CREATE_TABLE &&
      thd->lex->sql_command != SQLCOM_INSERT_SELECT)
    thd->abort_on_warning= thd->is_strict_mode();
  thd->count_cuted_fields= CHECK_FIELD_WARN;
  save_counter= thd->get_stmt_da()->set_current_row_for_warning(++row_counter);
  rc= select_unit::send_data(values);
  thd->get_stmt_da()->set_current_row_for_warning(save_counter);
  thd->count_cuted_fields= save_count_cuted_fields;
  thd->abort_on_warning= save_abort_on_warning;

  if (rc == 0 &&
      write_err != HA_ERR_FOUND_DUPP_KEY &&
      write_err != HA_ERR_FOUND_DUPP_UNIQUE)
  { 
    int err;
    DBUG_ASSERT(incr_table->s->reclength == table->s->reclength ||
               incr_table->s->reclength == table->s->reclength - MARIA_UNIQUE_HASH_LENGTH);
    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)
                         plus one for `ALL`

  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.func_count= tmp_table_param.field_count;
  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();

  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= incr_table_param.func_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();
  return false;
}


/*
  @brief
    Write a record

  @retval
    -2   conversion happened
    -1  found a duplicate key
    0   no error
    1   if an error is reported
*/

int select_unit::write_record()
{
  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
      */
      return -1;
    }
    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))
    {
      if (!create_internal_tmp_table_from_heap(thd, table,
                                              tmp_table_param.start_recinfo,
                                              &tmp_table_param.recinfo,
                                              write_err, 1, &is_duplicate))
        return -2;
      return 1;
    }
    if (is_duplicate)
      return -1;
  }
  return 0;
}


/*
  @brief
    Update counter for a record

  @retval
    0   no error
    -1  error occurred
*/

int select_unit::update_counter(Field* counter, longlong value)
{
  store_record(table, record[1]);
  counter->store(value, 0);
  int error= table->file->ha_update_tmp_row(table->record[1],
                                        table->record[0]);
  return error;
}


/*
  @brief
    Try to disable index
  
  @retval
    true    index is disabled and unfold is needed
    false   this time did not disable the index
*/

bool select_unit_ext::disable_index_if_needed(SELECT_LEX *curr_sl)
{
  const bool oracle_mode= (thd->variables.sql_mode & IS_OR_WAS_ORACLE);
  if (is_index_enabled && 
      ((!oracle_mode &&
        curr_sl == curr_sl->master_unit()->union_distinct) ||
        !curr_sl->next_select()) )
  {
    is_index_enabled= false;
    int error= table->file->ha_disable_indexes(key_map(0), false);
    if (error)
    {
      table->file->print_error(error, MYF(0));
      DBUG_ASSERT(0);
      return false;
    }
    table->no_keyread=1;
    /* In case of Oracle mode we unfold at the last operator */
    DBUG_ASSERT(!oracle_mode || !curr_sl->next_select());
    return !curr_sl->distinct;
  }
  return false;
}

/*
  @brief
    Unfold a record

  @retval
    0   no error
    -1  conversion happened
    1   error

    Note that duplicate keys are ignored (write_record() is returning -1)
*/

int select_unit_ext::unfold_record(ha_rows cnt)
{

  DBUG_ASSERT(cnt > 0);
  int ret= 0;
  while (--cnt)
  {
    int error= write_record();
    if (error == -2)
      ret= -1;                                  // Conversion happened
    else if (error > 0)
      return error;
  }
  return ret;
}

/*
  @brief
    Delete a record

  @retval
    0   no error
    1   if an error is reported
*/

int select_unit::delete_record()
{
  DBUG_ASSERT(!table->triggers);
  table->status|= STATUS_DELETED;
  int not_reported_error= table->file->ha_delete_tmp_row(table->record[0]);
  return MY_TEST(not_reported_error);
}

/**
  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::reset_for_next_ps_execution()
{
  table->file->extra(HA_EXTRA_RESET_STATE);
  table->file->ha_delete_all_rows();
}


/*
  @brief
    Set up value needed by send_data() and send_eof()

  @detail
    - For EXCEPT we will decrease the counter by one
    and INTERSECT / UNION we increase the counter.

    - For INTERSECT we will modify the second extra field (intersect counter)
    and for EXCEPT / UNION we modify the first (duplicate counter)
*/

void select_unit_ext::change_select()
{
  select_unit::change_select();
  switch(step){
  case UNION_TYPE:
    increment= 1;
    curr_op_type= UNION_DISTINCT;
    break;
  case EXCEPT_TYPE:
    increment= -1;
    curr_op_type= EXCEPT_DISTINCT;
    break;
  case INTERSECT_TYPE:
    increment= 1;
    curr_op_type= INTERSECT_DISTINCT;
    break;
  default: DBUG_ASSERT(0);
  }
  if (!thd->lex->current_select->distinct)
    /* change type from DISTINCT to ALL */
    curr_op_type= (set_op_type)(curr_op_type + 1);

  duplicate_cnt= table->field[addon_cnt - 1];
  if (addon_cnt == 2)
    additional_cnt= table->field[addon_cnt - 2];
  else
    additional_cnt= NULL;
}


/*
  @brief
    Fill temporary tables for operations need extra fields

  @detail
    - If this operation is not distinct, we try to find it and increase the
    counter by "increment" setted in select_unit_ext::change_select().

    - If it is distinct, for UNION we write this record; for INTERSECT we
    try to find it and increase the intersect counter if found; for EXCEPT
    we try to find it and delete that record if found.

*/

int select_unit_ext::send_data(List<Item> &values)
{
  int rc= 0;
  int not_reported_error= 0;
  int find_res;

  if (table->no_rows_with_nulls)
    table->null_catch_flags= CHECK_ROW_FOR_NULLS_TO_REJECT;

  fill_record(thd, table, table->field + addon_cnt, values, true, false, true);
  /* set up initial values for records to be written */
  if ( step == UNION_TYPE )
  {
    /* set duplicate counter to 1 */
    duplicate_cnt->store((longlong) 1, 1);
    /* set the other counter to 0 */
    if (curr_op_type == INTERSECT_ALL)
      additional_cnt->store((longlong) 0, 1);
  }

  if (unlikely(thd->is_error()))
  {
    rc= 1;
    if (unlikely(not_reported_error))
    {
      DBUG_ASSERT(rc);
      table->file->print_error(not_reported_error, MYF(0));
    }
    return rc;
  }
  if (table->no_rows_with_nulls)
  {
    table->null_catch_flags&= ~CHECK_ROW_FOR_NULLS_TO_REJECT;
    if (table->null_catch_flags)
    {
      if (unlikely(not_reported_error))
      {
        DBUG_ASSERT(rc);
        table->file->print_error(not_reported_error, MYF(0));
      }
      return rc;
    }
  }

  switch(curr_op_type)
  {
  case UNION_ALL:
    if (!is_index_enabled ||
      (find_res= table->file->find_unique_row(table->record[0], 0)))
    {
      rc= write_record();
      /* no reaction with conversion */
      if (rc == -2)
        rc= 0;
    }
    else
    {
      longlong cnt= duplicate_cnt->val_int() + increment;
      not_reported_error= update_counter(duplicate_cnt, cnt);
      DBUG_ASSERT(!table->triggers);
      rc= MY_TEST(not_reported_error);
    }
    break;

  case EXCEPT_ALL:
    if (!(find_res= table->file->find_unique_row(table->record[0], 0)))
    {
      longlong cnt= duplicate_cnt->val_int() + increment;
      if (cnt == 0)
        rc= delete_record();
      else
      {
        not_reported_error= update_counter(duplicate_cnt, cnt);
        DBUG_ASSERT(!table->triggers);
        rc= MY_TEST(not_reported_error);
      }
    }
    break;

  case INTERSECT_ALL:
    if (!(find_res= table->file->find_unique_row(table->record[0], 0)))
    {
      longlong cnt= duplicate_cnt->val_int() + increment;
      if (cnt <= additional_cnt->val_int())
      {
        not_reported_error= update_counter(duplicate_cnt, cnt);
        DBUG_ASSERT(!table->triggers);
        rc= MY_TEST(not_reported_error);
      }
    }
    break;

  case UNION_DISTINCT:
    rc= write_record();
    /* no reaction with conversion */
    if (rc == -2)
      rc= 0;
    break;

  case EXCEPT_DISTINCT:
    if (!(find_res= table->file->find_unique_row(table->record[0], 0)))
      rc= delete_record();
    else
      rc= not_reported_error= (find_res != 1);
    break;

  case INTERSECT_DISTINCT:
    if (!(find_res= table->file->find_unique_row(table->record[0], 0)))
    {
      if (additional_cnt->val_int() == prev_step)
      {
        not_reported_error= update_counter(additional_cnt, curr_step);
        rc= MY_TEST(not_reported_error);
        DBUG_ASSERT(rc != HA_ERR_RECORD_IS_THE_SAME);
      }
      else if (additional_cnt->val_int() != curr_step)
        rc= delete_record();
    }
    else
      rc= not_reported_error= (find_res != 1);
    break;

  default:
    DBUG_ASSERT(0);
  }

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


/*
  @brief
    Do post-operation after a operator

  @detail
    We need to scan in these cases:
      - If this operation is DISTINCT and next is ALL,
        duplicate counter needs to be set to 1.
      - If this operation is INTERSECT ALL and counter needs to be updated.
      - If next operation is INTERSECT ALL,
        set up the second extra field (called "intersect_counter") to 0.
        this extra field counts records in the second operand.

    If this operation is equal to "union_distinct" or is the last operation,
    we'll disable index. Then if this operation is ALL we'll unfold records.
*/

bool select_unit_ext::send_eof()
{
  int error= 0;
  SELECT_LEX *curr_sl= thd->lex->current_select;
  SELECT_LEX *next_sl= curr_sl->next_select();
  bool is_next_distinct= next_sl && next_sl->distinct;
  bool is_next_intersect_all=
                        next_sl &&
                        next_sl->get_linkage() == INTERSECT_TYPE &&
                        !next_sl->distinct;
  /*
    True at the last INTERSECT of an inline INTERSECT DISTINCT subsequence: the
    records that did not match every operand (their intersect counter differs
    from curr_step) must be dropped. Instead of a separate table scan this is
    folded into the scan/unfold loops below, so the table is scanned only once
    (MDEV-38722). When the subsequence is materialized in a derived table this
    filtering is done by select_unit::send_eof() instead.
  */
  bool filter_intersect= curr_op_type == INTERSECT_DISTINCT &&
                         !(next_sl &&
                           next_sl->get_linkage() == INTERSECT_TYPE);
  bool need_unfold= disable_index_if_needed(curr_sl);

  if (((curr_sl->distinct && !is_next_distinct) ||
      curr_op_type == INTERSECT_ALL ||
      filter_intersect ||
      is_next_intersect_all) &&
      !need_unfold)
  {
    if (!next_sl)
      DBUG_ASSERT((thd->variables.sql_mode & MODE_ORACLE) ||
                  curr_op_type != INTERSECT_ALL);
    bool need_update_row;
    if (unlikely(table->file->ha_rnd_init_with_error(1)))
      return 1;
    do
    {
      need_update_row= false;
      if (unlikely(error= table->file->ha_rnd_next(table->record[0])))
      {
        if (error == HA_ERR_END_OF_FILE)
        {
          error= 0;
          break;
        }
        break;
      }
      if (filter_intersect && additional_cnt->val_int() != curr_step)
      {
        /* drop a record that did not match every INTERSECT operand */
        if (unlikely(error= delete_record()))
          break;
        continue;
      }
      store_record(table, record[1]);

      if (curr_sl->distinct && !is_next_distinct)
      {
        /* set duplicate counter to 1 if next operation is ALL */
        duplicate_cnt->store(1, 0);
        need_update_row= true;
      }

      if (is_next_intersect_all)
      {
        longlong d_cnt_val= duplicate_cnt->val_int();
        if (d_cnt_val == 0)
          error= delete_record();
        else
        {
          if (curr_op_type == INTERSECT_ALL)
          {
            longlong a_cnt_val= additional_cnt->val_int();
            if (a_cnt_val < d_cnt_val)
              d_cnt_val= a_cnt_val;
          }
          additional_cnt->store(d_cnt_val, 0);
          duplicate_cnt->store((longlong)0, 0);
          need_update_row= true;
        }
      }

      if (need_update_row)
        error= table->file->ha_update_tmp_row(table->record[1],
                                              table->record[0]);
    } while (likely(!error));
    table->file->ha_rnd_end();
  }

  /*  unfold */
  else if (need_unfold)
  {
    /* unfold if is ALL operation */
    ha_rows dup_cnt;
    if (unlikely(table->file->ha_rnd_init_with_error(1)))
      return 1;
    do
    {
      if (unlikely(error= table->file->ha_rnd_next(table->record[0])))
      {
        if (error == HA_ERR_END_OF_FILE)
        {
          error= 0;
          break;
        }
        break;
      }
      if (filter_intersect && additional_cnt->val_int() != curr_step)
      {
        /* drop a record that did not match every INTERSECT operand */
        if (unlikely(error= delete_record()))
          break;
        continue;
      }
      dup_cnt= (ha_rows)duplicate_cnt->val_int();
      /* delete record if not exist in the second operand */
      if (dup_cnt == 0)
      {
        error= delete_record();
        continue;
      }
      if (curr_op_type == INTERSECT_ALL)
      {
        ha_rows add_cnt= (ha_rows)additional_cnt->val_int();
        if (dup_cnt > add_cnt && add_cnt > 0)
          dup_cnt= (ha_rows)add_cnt;
      }

      if (dup_cnt == 1)
        continue;

      duplicate_cnt->store((longlong)1, 0);
      if (additional_cnt)
        additional_cnt->store((longlong)0, 0);
      error= table->file->ha_update_tmp_row(table->record[1],
                                            table->record[0]);
      if (unlikely(error))
        break;

      if ((error= unfold_record(dup_cnt)) == -1)
      {
        /* restart the scan */
        if (unlikely(table->file->ha_rnd_init_with_error(1)))
          return 1;

        duplicate_cnt= table->field[addon_cnt - 1];
        if (addon_cnt == 2)
          additional_cnt= table->field[addon_cnt - 2];
        else
          additional_cnt= NULL;
        error= 0;
        continue;
      }
      else if (error > 0)
      {
        table->file->ha_index_or_rnd_end();
        return 1;
      }
    } while (likely(!error));
    table->file->ha_rnd_end();
  }

  /* Clean up table buffers for the next set operation from pipeline */
  if (next_sl)
    restore_record(table,s->default_values);

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

  return (MY_TEST(error));
}

void select_union_recursive::reset_for_next_ps_execution()
{
  if (table)
  {
    select_unit::reset_for_next_ps_execution();
    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;
  }
  row_counter= 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, true);
  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->killed == ABORT_QUERY)
  {
    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.insert(&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;
  }
}


bool st_select_lex_unit::prepare_join(THD *thd_arg, SELECT_LEX *sl,
                                      select_result *tmp_result,
                                      ulonglong 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->limit_params.explicit_limit) &&
                      !thd->lex->with_rownum);

  saved_error= join->prepare(sl->table_list.first,
                             (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);

  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, 0, 0);
    }
  }
  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);
}


static bool init_item_int(THD* thd, Item_int* &item)
{
  if (!item)
  {
    item= new (thd->mem_root) Item_int(thd, 0);

    if (!item)
      return true;
  }
  else
  {
    item->value= 0;
  }

  return false;
}

/**
  @brief
    Recursive subroutine to be called from find_unit_handler() (see below).
    Must not be called directly, only from find_unit_handler().
*/
static select_handler *find_unit_handler_for_lex(THD *thd,
                                                 SELECT_LEX *sel_lex,
                                                 SELECT_LEX_UNIT* unit)
{
  if (!(sel_lex->join))
    return nullptr;
  for (TABLE_LIST *tbl= sel_lex->join->tables_list; tbl; tbl= tbl->next_local)
  {
    if (!tbl->table)
      continue;
    if (tbl->derived)
    {
      /*
        Skip derived table for now as they will be checked
        in the subsequent loop
      */
      continue;
    }
    handlerton *ht= tbl->table->file->partition_ht();
    if (!ht->create_unit)
      continue;
    select_handler *sh= ht->create_unit(thd, unit);
    if (sh)
      return sh;
  }

  for (SELECT_LEX_UNIT *un= sel_lex->first_inner_unit(); un;
       un= un->next_unit())
  {
    for (SELECT_LEX *sl= un->first_select(); sl; sl= sl->next_select())
    {
      select_handler *uh= find_unit_handler_for_lex(thd, sl, unit);
      if (uh)
        return uh;
    }
  }
  return nullptr;
}


/**
  @brief
    Look for provision of the select_handler interface by a foreign engine.
    This interface must support processing UNITs (multiple SELECTs combined
    with UNION/EXCEPT/INTERSECT operators)

  @param
    thd   The thread handler
    unit  UNIT (one or more SELECTs combined with UNION/EXCEPT/INTERSECT

  @details
    The function checks that this is an upper level UNIT and if so looks
    through its tables searching for one whose handlerton owns a
    create_unit call-back function. If the call of this function returns
    a select_handler interface object then the server will push the
    query into this engine.
    This is a responsibility of the create_unit call-back function to
    check whether the engine can execute the query.

    The function recursively scans subqueries (see find_unit_handler_for_lex())
    to get down to real tables and process queries like this:
      (SELECT a FROM t1 UNION SELECT b FROM t2) UNION
        (SELECT c FROM t3 UNION select d FROM t4)

  @retval the found select_handler if the search is successful
          nullptr  otherwise
*/

static select_handler *find_unit_handler(THD *thd,
                                         SELECT_LEX_UNIT *unit)
{
  if (unit->outer_select())
    return nullptr;

  for (SELECT_LEX *sl= unit->first_select(); sl; sl= sl->next_select())
  {
    select_handler *uh= find_unit_handler_for_lex(thd, sl, unit);
    if (uh)
      return uh;
  }
  return nullptr;
}


inline bool st_select_lex_unit::rename_item_list(TABLE_LIST *derived_arg)
{
  if (derived_arg->save_original_names(first_select()))
    return true;
  if (first_select()->set_item_list_names(derived_arg->column_names))
    return true;
  return false;
}


inline bool st_select_lex_unit::rename_types_list(List<Lex_ident_sys> *newnames)
{
  if (item_list.elements != newnames->elements)
  {
    my_error(ER_INCORRECT_COLUMN_NAME_COUNT, MYF(0));
    return true;
  }

  List_iterator<Lex_ident_sys> it(*newnames);
  List_iterator_fast<Item> li(types);
  Item *item;

  while ((item= li++))
    lex_string_set( &item->name, (it++)->str);

  return false;
}


bool st_select_lex_unit::prepare(TABLE_LIST *derived_arg,
                                 select_result *sel_result,
                                 ulonglong 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;
  have_except_all_or_intersect_all= false;
  bool instantiate_tmp_table= false;
  bool use_direct_union_result= false;
  bool single_tvc= !first_sl->next_select() && first_sl->tvc;
  bool single_tvc_wo_order= single_tvc && !first_sl->order_list.elements;
  bool distinct_key= 0;
  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;
          lim.clear();
   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()->optimize_out_order_list();
  }

  /* will only optimize once */
  if (!bag_set_op_optimized && !is_recursive)
  {
    optimize_bag_operation(false);
  }

  for (SELECT_LEX *s= first_sl; s; s= s->next_select())
  {
    switch (s->linkage)
    {
    case INTERSECT_TYPE:
      have_intersect= TRUE;
      if (!s->distinct)
        have_except_all_or_intersect_all= TRUE;
      break;
    case EXCEPT_TYPE:
      have_except= TRUE;
      if (!s->distinct)
        have_except_all_or_intersect_all= TRUE;
      break;
    case DERIVED_TABLE_TYPE:
      if (s->distinct)
        distinct_key= 1;
      break;
    default:
      break;
    }
  }

  if (is_union_select || is_recursive)
  {
    if ((single_tvc_wo_order && !fake_select_lex) ||
        (is_unit_op() && !union_needs_tmp_table() &&
         !have_except && !have_intersect && !single_tvc))
    {
      if (unlikely(set_direct_union_result(sel_result)))
        goto err;
      tmp_result= union_result;
      fake_select_lex= NULL;
      instantiate_tmp_table= false;
      use_direct_union_result= true;
    }
    else
    {
      if (!is_recursive)
      {
        /*
          class "select_unit_ext" handles query contains EXCEPT ALL and / or
          INTERSECT ALL. Others are handled by class "select_unit"
          If have EXCEPT ALL or INTERSECT ALL in the query. First operand
          should be UNION ALL
        */
        if (have_except_all_or_intersect_all)
        {
          union_result= new (thd->mem_root) select_unit_ext(thd);
          first_sl->distinct= false;
        }
        else
   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->limit_params.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;
  }

  if (sl->tvc && sl->order_list.elements &&
      !sl->tvc->to_be_wrapped_as_with_tail())
  {
    SELECT_LEX_UNIT *unit= sl->master_unit();
    if (thd->lex->context_analysis_only & CONTEXT_ANALYSIS_ONLY_VIEW)
    {
      unit->fake_select_lex= 0;
      unit->saved_fake_select_lex= 0;
    }
    else
    {
      if (!unit->first_select()->next_select())
      {
        if (!unit->fake_select_lex)
        {
          Query_arena *arena, backup_arena;
          arena= thd->activate_stmt_arena_if_needed(&backup_arena);
          bool rc= unit->add_fake_select_lex(thd);
          if (arena)
            thd->restore_active_arena(arena, &backup_arena);
          if (rc)
            goto err;
        }
        SELECT_LEX *fake= unit->fake_select_lex;
        fake->order_list= sl->order_list;
        fake->limit_params= sl->limit_params;
        sl->order_list.empty();
        sl->limit_params.clear();
        if (describe)
          fake->options|= SELECT_DESCRIBE;
      }
      else if (!sl->limit_params.explicit_limit)
        sl->order_list.empty();
    }
  }

  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 second 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->process_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) ||
                                               distinct_key),
                                              create_options,
                                              &derived_arg->alias, false,
                                              instantiate_tmp_table, false,
                                              0))
          goto err;
        if (have_except_all_or_intersect_all)
        {
          union_result->init();
        }
        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,
                                                            distinct_key,
                                                            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;
      }
    }      
  }

  /*
    We need to rename tvc BEFORE Item_holder pushed into result table
    below in join_union_item_types().
  */
  if (first_select()->tvc && derived_arg && derived_arg->column_names)
    if (rename_item_list(derived_arg))
      goto err;

  // 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++))
    {
      /*
        Test if the aggregated data type is OK for a UNION element.
        E.g. in case of string data, DERIVATION_NONE is not allowed.
      */
      if (type->type() == Item::TYPE_HOLDER && type->type_handler()->
            union_element_finalize(static_cast<Item_type_holder*>(type)))
        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, &ft, 0))
        {
          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
      fulltext 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;

    /* extra field counter */
    uint hidden= 0;
    Item_int *addon_fields[2]= {0};
    if (!is_recursive)
    {
      if (have_except_all_or_intersect_all)
      {
        /* add duplicate_count */
        ++hidden;
      }
      /* add intersect_count */
      if (have_intersect)
        ++hidden;

      for(uint i= 0; i< hidden; i++)
      {
        if (init_item_int(thd, addon_fields[i]) ||
            types.push_front(addon_fields[i]))
        {
          types.empty();
          goto err;
        }
        addon_fields[i]->name.str= i ? "__CNT_1" : "__CNT_2";
        addon_fields[i]->name.length= 7;
      }
      bool error=
        union_result->create_result_table(thd, &types,
                                          MY_TEST(union_distinct) ||
                                            have_except_all_or_intersect_all ||
                                            have_intersect || distinct_key,
                                          create_options, &empty_clex_str,
                                          false, instantiate_tmp_table, false,
                                          hidden);
      union_result->addon_cnt= hidden;
      for (uint i= 0; i < hidden; i++)   
        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);
      for (uint i= 0; i < hidden; i++)
        item_list.pop();

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

      if (unlikely(saved_error))
        goto err;
    }
    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, hidden);
    }

    if (fake_select_lex != NULL)
    {
      init_prepare_fake_select_lex(thd, TRUE);

      DBUG_ASSERT(fake_select_lex->join == 0);
      if (!(fake_select_lex->join= new JOIN(thd, item_list, options, 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;
      fake_select_lex->join->no_const_tables= TRUE;
      saved_error= fake_select_lex->join->prepare(
          fake_select_lex->table_list.first, 0,
                global_parameters()->order_list.elements, // og_num
                global_parameters()->order_list.first,    // order
                false, NULL, NULL, NULL, fake_select_lex, this);
    }
    /*
      Rename types used in result table for union.
    */
    if (derived_arg && derived_arg->column_names)
    {
      if (rename_types_list(derived_arg->column_names))
        goto err;
    }

    if (!thd->lex->is_view_context_analysis())
      pushdown_unit= find_unit_handler(thd, this);
    if (pushdown_unit)
    {
      if (prepare_pushdown(use_direct_union_result, sel_result))
        goto err;
    }
  }

  if (derived_arg && derived_arg->column_names)
  {
    if (rename_item_list(derived_arg))
      goto err;
  }

  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);
}

/**
  @brief
    Prepare st_select_lex_unit for the pushdown handler processing
  @details
    Creates and initializes data structures required for processing of the
    pushdown handler. Validates fake_select_lex then discards it and sets
    direct union result which is necessary for pushed down statements
  @return
    false - success
    true - failure
*/
bool st_select_lex_unit::prepare_pushdown(bool use_direct_union_result,
                                          select_result *sel_result)
{
  if (unlikely(pushdown_unit->prepare()))
    return true;

  if(!use_direct_union_result)
  {
    /*
      Always use select_union_direct result for pushed down units, overwrite
      the previous union_result unless select_union_direct is already used
    */
    if (unlikely(set_direct_union_result(sel_result)))
      return true;
  }
  return false;
}


bool st_select_lex_unit::set_direct_union_result(select_result *sel_result)
{
  SELECT_LEX *last= first_select();
  while (last->next_select())
    last= last->next_select();
  union_result= new (thd->mem_root) select_union_direct(thd, sel_result,
                                                      last);
  return (union_result == nullptr);
}

/**
  @brief
    Optimize a sequence of set operations

  @param first_sl first select of the level now under processing

  @details
    The method optimizes with the following rules:
    - (1)If a subsequence of INTERSECT contains at least one INTERSECT DISTINCT
        or this subsequence is followed by UNION/EXCEPT DISTINCT then all
        elements in the subsequence can changed for INTERSECT DISTINCT
    - (2)If previous set operation is DISTINCT then EXCEPT ALL can be replaced
        for EXCEPT DISTINCT
    - (3)If UNION DISTINCT / EXCEPT DISTINCT follows a subsequence of UNION ALL
        then all set operations of this subsequence can be replaced for
        UNION DISTINCT

    For derived table it will look up outer select, and do optimize based on
    outer select.

    Variable "union_distinct" will be updated in the end.
    Not compatible with Oracle Mode.
*/

void st_select_lex_unit::optimize_bag_operation(bool is_outer_distinct)
{
  /*
    skip run optimize for:
      ORACLE MODE
      CREATE VIEW
      PREPARE ... FROM
      recursive
  */
  if ((thd->variables.sql_mode & IS_OR_WAS_ORACLE) ||
    (thd->lex->context_analysis_only & CONTEXT_ANALYSIS_ONLY_VIEW) ||
    (fake_select_lex != NULL && thd->stmt_arena->is_stmt_prepare()) ||
    (with_element && with_element->is_recursive ))
    return;
  DBUG_ASSERT(!bag_set_op_optimized);

  SELECT_LEX *sl;
  /* INTERSECT subsequence can occur only at the very beginning */
  /* The first select with linkage == INTERSECT_TYPE */
  SELECT_LEX *intersect_start= NULL;
  /* The first select after the INTERSECT subsequence */
  SELECT_LEX *intersect_end= NULL;
  /*
    Will point to the last node before UNION ALL subsequence.
    Index can be disable there.
  */
  SELECT_LEX *disable_index= NULL;
  /*
    True if there is a select with:
    linkage == INTERSECT_TYPE && distinct==true
  */
  bool any_intersect_distinct= false;
  SELECT_LEX *prev_sl= first_select();

  /* process INTERSECT subsequence in the begining */
  for (sl= prev_sl->next_select(); sl; prev_sl= sl, sl= sl->next_select())
  {
    if (sl->linkage != INTERSECT_TYPE)
    {
      intersect_end= sl;
      break;
    }
    else
    {
      if (!intersect_start)
        intersect_start= sl;
      if (sl->distinct)
      {
        any_intersect_distinct= true;
        disable_index= sl;
      }
    }
  }

  /* if subquery only contains INTERSECT and outer is UNION DISTINCT*/
  if (!sl && is_outer_distinct)
    any_intersect_distinct= true;

  /* The first select of the current UNION ALL subsequence */
  SELECT_LEX *union_all_start= NULL;
  for ( ; sl; prev_sl= sl, sl= sl->next_select())
  {
    DBUG_ASSERT (sl->linkage != INTERSECT_TYPE);
    if (!sl->distinct)
    {
      if (sl->linkage == UNION_TYPE)
      {
        if (!union_all_start)
        {
          union_all_start= sl;
        }
      }
      else
      {
        DBUG_ASSERT (sl->linkage == EXCEPT_TYPE);
        union_all_start= NULL;
        if (prev_sl->distinct && prev_sl->is_set_op())
        {
          sl->distinct= true;
          disable_index= sl;
        }
        else if (disable_index)
        {
          /*
            EXCEPT ALL needs the unique index in select_unit_ext::send_data().
            If the index would otherwise be released at an earlier node,
            postpone the release until (at least) this operation.
          */
          disable_index= sl;
        }
      }
    }
    else
    { /* sl->distinct == true */
      for (SELECT_LEX *si= union_all_start; si && si != sl; si= si->next_select())
      {
          si->distinct= true;
      }
      union_all_start= NULL;
      disable_index= sl;
    }
  }

  if (is_outer_distinct)
  {
    for (SELECT_LEX *si= union_all_start; si && si != sl; si= si->next_select())
    {
        si->distinct= true;
    }
    union_all_start= NULL;
  }

  if (any_intersect_distinct ||
      (intersect_end != NULL && intersect_end->distinct))
  {
    for (sl= intersect_start; sl && sl != intersect_end; sl= sl->next_select())
    {
      sl->distinct= true;
      if (disable_index && disable_index->linkage == INTERSECT_TYPE)
        disable_index= sl;
    }
  }
  /*
    if disable_index points to a INTERSECT, based on rule 1 we can set it
    to the last INTERSECT node.
  */
  if (disable_index && disable_index->linkage == INTERSECT_TYPE &&
    intersect_end && intersect_end->distinct)
    disable_index= intersect_end;
  /* union_distinct controls when to disable index */
  union_distinct= disable_index;

  /* recursive call this function for whole lex tree */
  for(sl= first_select(); sl; sl= sl->next_select())
  {
    if (sl->is_unit_nest() &&
        sl->first_inner_unit() &&
        !sl->first_inner_unit()->bag_set_op_optimized)
      sl->first_inner_unit()->optimize_bag_operation(sl->distinct);
  }

  /* mark as optimized */
  bag_set_op_optimized= 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 & reexecute 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_result->force_enable_index_if_needed() || union_distinct))
      {
        if(table->file->ha_enable_indexes(key_map(table->s->keys), false))
          DBUG_ASSERT(0);
        else
          table->no_keyread= 0;
      }
    }
    for (SELECT_LEX *sl= select_cursor; sl; sl= sl->next_select())
    {
      if (sl->tvc)
      {
 sl->tvc->select_options=
          (lim.is_unlimited() || 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)
 {
          lim.remove_offset();
   /*
     We can't use LIMIT at this stage if we are using ORDER BY for the
     whole query
  */
   if (sl->order_list.first || describe)
            lim.set_unlimited();
        }

        /*
          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=
          (lim.is_unlimited() || sl->braces) ?
          sl->options & ~OPTION_FOUND_ROWS : sl->options | found_rows_for_union;

        if (!this->pushdown_unit)
        {
          /*
            If the UNIT hasn't been pushed down to the engine as a whole,
            try to push down partial SELECTs of this UNIT separately
          */
          sl->pushdown_select= find_partial_select_handler(thd, sl, this);
        }

 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()
{
  DBUG_ENTER("st_select_lex_unit::exec");
  if (executed && !uncacheable && !describe)
    DBUG_RETURN(FALSE);

  if (pushdown_unit)
  {
    create_explain_query_if_not_exists(thd->lex, thd->mem_root);
    if (!executed)
      save_union_explain(thd->lex->explain);
    DBUG_RETURN(pushdown_unit->execute());
  }
  DBUG_RETURN(exec_inner());
}


bool st_select_lex_unit::exec_inner()
{
  SELECT_LEX *lex_select_save= thd->lex->current_select;
  SELECT_LEX *select_cursor=first_select();
  ulonglong add_rows=0;
  bool first_execution= !executed;
  bool was_executed= executed;
  int error;

  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);

  error= saved_error;

  if (unlikely(error))
  {
  err:
    thd->lex->current_select= lex_select_save;
    return 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(key_map(table->s->keys), false);
    }
  }

  if (uncacheable || !item || !item->assigned() || describe)
  {
    if (!fake_select_lex && !(with_element && with_element->is_recursive))
      union_result->reset_for_next_ps_execution();
    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->first_select_lex())
          fake_select_lex->uncacheable|= sl->uncacheable;
        else
          fake_select_lex->uncacheable= 0;
      }

      {
        set_limit(sl);
 if (sl == global_parameters() || describe)
 {
   lim.remove_offset();
   /*
     We can't use LIMIT at this stage if we are using ORDER BY for the
     whole query
  */
   if (sl->order_list.first || describe)
     lim.set_unlimited();
        }

        /*
          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=
             (lim.is_unlimited() || sl->braces) ?
             sl->options & ~OPTION_FOUND_ROWS : sl->options | found_rows_for_union;
   saved_error= sl->tvc->optimize(thd);
 }
 else
 {
          sl->join->select_options=
            (lim.is_unlimited() || 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;

        /* select_unit::send_data() writes rows to (temporary) table */
 if (sl->tvc)
   sl->tvc->exec(sl);
 else
   saved_error= sl->join->exec();
        /*
          Allow UNION ALL to work: disable unique key. We cannot disable indexes
          in the middle of the query because enabling indexes requires table to be empty
          (see heap_enable_indexes()). So there is special union_distinct property
          which is the rightmost distinct UNION in the expression and we release
          the unique key after the last (rightmost) distinct UNION, therefore only the
          subsequent UNION ALL work as non-distinct.
        */
        if (sl == union_distinct && !have_except_all_or_intersect_all &&
            !(with_element && with_element->is_recursive))
 {
          // This is UNION DISTINCT, so there should be a fake_select_lex
          DBUG_ASSERT(fake_select_lex != NULL);
          error= table->file->ha_disable_indexes(key_map(0), false);
          if (error)
          {
            table->file->print_error(error, MYF(0));
            DBUG_ASSERT(0);
            error= true;
            goto err;
          }
   table->no_keyread=1;
 }
 if (likely(!saved_error))
 {
   if (union_result->flush())
   {
            error= true;
            goto err;
   }
 }
      }
      if (unlikely(saved_error))
      {
        error= saved_error;
        goto err;
      }
      if (fake_select_lex != NULL)
      {
        /* Needed for the following test and for records_at_start in next loop */
        error= table->file->info(HA_STATUS_VARIABLE);
        if (unlikely(error))
        {
          table->file->print_error(error, MYF(0));
          goto err;
        }
      }
      if (found_rows_for_union && !sl->braces &&
          !lim.is_unlimited())
      {
 /*
   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.
        */
        thd->reset_killed();
        break;
      }
    }
  }

  DBUG_EXECUTE_IF("show_explain_probe_union_read", 
                   dbug_serve_apcs(thd, 1););
  /*
    Temporarily deactivate LIMIT ROWS EXAMINED to avoid producing potentially
    incomplete result of the UNION due to exceeding of the limit. It will be
    re-activated upon the function exit
  */
  const bool limit_rows_was_activated=
    thd->lex->deactivate_limit_rows_examined();

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

      set_limit(global_parameters());
      JOIN *join= fake_select_lex->join;
      saved_error= false;
      if (!(thd->stmt_arena->is_stmt_prepare() ||
           (thd->lex->context_analysis_only & CONTEXT_ANALYSIS_ONLY_VIEW)) &&
          first_execution)
      {
        save_union_explain_part2(thd->lex->explain);

        saved_error= mysql_select(thd, &result_table_list,
                                  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?? 
          saved_error= mysql_select(thd, &result_table_list, 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
        {
          saved_error= join->reinit();
          if (join->exec())
            saved_error= 1;
        }
      }

      fake_select_lex->table_list.empty();
      if (likely(!saved_error))
        thd->limit_found_rows= (ulonglong)table->file->stats.records + add_rows;
      /*
 Mark for slow query log if any of the union parts didn't use
 indexes efficiently
      */
  }
  thd->lex->current_select= lex_select_save;
  if (limit_rows_was_activated)
    thd->lex->set_limit_rows_examined();
  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;
  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
    {
      saved_error= sl->join->exec();
    }
    if (likely(!saved_error))
    {
       if (unlikely(union_result->flush()))
       {
  thd->lex->current_select= lex_select_save;
  DBUG_RETURN(1);
       }
    }
    else
    {
      thd->lex->current_select= lex_select_save;
      goto err;
    }
  }

  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:
  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 &&
      with_element->rec_outer_references)
  {
    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)
        if (with_elem->rec_result)
          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)->reset_for_next_ps_execution();
      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
    }
  }

  delete pushdown_unit;
  pushdown_unit= nullptr;

  /*
    Cleanup stranded units only after this unit has completed its own
    cleanup, ensuring a parent-first (LIFO) cleanup order for merged tables.
  */
  cleanup_stranded_units();
  /*
    Cleanup stranded units only after this unit has completed its own
    cleanup, ensuring a parent-first (LIFO) cleanup order for merged tables.
  */
  cleanup_stranded_units();

  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 (fake_select_lex && fake_select_lex->join)
    fake_select_lex->join->change_result(new_result, old_result);
  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;
}


static void cleanup_window_funcs(List<Item_window_func> &win_funcs)
{
  List_iterator_fast<Item_window_func> it(win_funcs);
  Item_window_func *win_func;
  while ((win_func= it++))
  {
    Window_spec *win_spec= win_func->window_spec;
    if (!win_spec)
      continue;
    if (win_spec->save_partition_list)
    {
      win_spec->partition_list= win_spec->save_partition_list;
      win_spec->save_partition_list= NULL;
    }
    if (win_spec->save_order_list)
    {
      win_spec->order_list= win_spec->save_order_list;
      win_spec->save_order_list= NULL;
    }
  }
}


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

  DBUG_PRINT("info", ("select: %p (%u)  JOIN %p",
                      this, select_number, join));
  cleanup_order(order_list.first);
  cleanup_order(group_list.first);
  cleanup_ftfuncs(this);

  cleanup_window_funcs(window_funcs);

  /*
    In UPDATE/DELETE, it can be that leaf_tables has tables while the JOIN
    object is not created yet (and then some error occurs and we get here).
    In leaf_tables, recursive CTE references need cleanup.
  */
  if (leaf_tables.elements)
  {
    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();
      }
    }
  }

  if (join)
  {
    DBUG_ASSERT((st_select_lex*)join->select_lex == this);
    error|= (bool)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 &&
        lex_unit->with_element->rec_outer_references)
      continue;
    error= (bool) ((uint) error | (uint) lex_unit->cleanup());
  }
  inner_refs_list.empty();
  exclude_from_table_unique_test= FALSE;
  hidden_bit_fields= 0;
  delete pushdown_select;
  pushdown_select= nullptr;
  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() &&
      union_distinct->distinct)
    return true;
  return false;
}