Method exec_inner

sql/sql_union.cc:2354–2599

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;
      }