Method print_explain_regular

sql/sql_explain.cc:600–706

*/

int Explain_union::print_explain_regular(Explain_query *query,
                                 select_result_sink *output,
                                 uint8 explain_flags, 
                                 bool is_analyze)
{
  THD *thd= output->thd;
  MEM_ROOT *mem_root= thd->mem_root;
  char table_name_buffer[SAFE_NAME_LEN];

  /* print all UNION children, in order */
  for (int i= 0; i < (int) union_members.elements(); i++)
  {
    Explain_select *sel= query->get_select(union_members.at(i));
    sel->print_explain(query, output, explain_flags, is_analyze);
  }

  if (!using_tmp)
  {
    /*
      The union operation may not employ a temporary table, for example,
      for UNION ALL, in that case the results of the query are sent directly
      to the output. So there is no actual UNION operation and we don't need
      to print the line in the EXPLAIN output.
    */
    return 0;
  }

  /* Print a line with "UNIT RESULT" */
  List<Item> item_list;
  Item *item_null= new (mem_root) Item_null(thd);

  /* `id` column */
  item_list.push_back(item_null, mem_root);

  /* `select_type` column */
  push_str(thd, &item_list, fake_select_type);

  /* `table` column: something like "<union1,2>" */
  uint len= make_union_table_name(table_name_buffer);
  item_list.push_back(new (mem_root)
                      Item_string_sys(thd, table_name_buffer, len),
                      mem_root);

  /* `partitions` column */
  if (explain_flags & DESCRIBE_PARTITIONS)
    item_list.push_back(item_null, mem_root);

  /* `type` column */
  push_str(thd, &item_list, join_type_str[JT_ALL]);

  /* `possible_keys` column */
  item_list.push_back(item_null, mem_root);

  /* `key` */
  item_list.push_back(item_null, mem_root);

  /* `key_len` */
  item_list.push_back(item_null, mem_root);