Method start

sql/sql_select.cc:22053–22211

*/

TABLE *Create_tmp_table::start(THD *thd,
                               TMP_TABLE_PARAM *param,
                               const LEX_CSTRING *table_alias)
{
  MEM_ROOT *mem_root_save, own_root;
  TABLE *table;
  TABLE_SHARE *share;
  uint  copy_func_count= param->func_count;
  char  *tmpname,path[FN_REFLEN];
  Field **reg_field;
  uint *blob_field;
  key_part_map *const_key_parts;
  /* Treat sum functions as normal ones when loose index scan is used. */
  m_save_sum_fields|= param->precomputed_group_by;
  DBUG_ENTER("Create_tmp_table::start");
  DBUG_PRINT("enter",
             ("table_alias: '%s'  distinct: %d  save_sum_fields: %d  "
              "rows_limit: %lu  group: %d", table_alias->str,
              (int) m_distinct, (int) m_save_sum_fields,
              (ulong) m_rows_limit, MY_TEST(m_group)));

  if (use_temp_pool && !(test_flags & TEST_KEEP_TMP_TABLES))
    m_temp_pool_slot = temp_pool_set_next();

  if (m_temp_pool_slot != MY_BIT_NONE) // we got a slot
    snprintf(path, sizeof(path), "%s-%s-%lx-%i", tmp_file_prefix, param->tmp_name,
             current_pid, m_temp_pool_slot);
  else
  {
    /* if we run out of slots or we are not using tempool */
    LEX_STRING tmp= {path, sizeof(path) };
    make_tmp_table_name(thd, &tmp, param->tmp_name);
  }

  /*
    No need to change table name to lower case as we are only creating
    MyISAM, Aria or HEAP tables here
  */
  fn_format(path, path, mysql_tmpdir, "", MY_REPLACE_EXT|MY_UNPACK_FILENAME);

  if (m_group)
  {
    ORDER **prev= &m_group;
    if (!param->quick_group)
      m_group= 0;                               // Can't use group key
    else for (ORDER *tmp= m_group ; tmp ; tmp= tmp->next)
    {
      /* Exclude found constant from the list */
      if ((*tmp->item)->const_item())
      {
        *prev= tmp->next;
        param->group_parts--;
        continue;
      }
      else
        prev= &(tmp->next);
      /*
        marker == 4 means two things: