Method register_sum_func

sql/item_sum.cc:263–324

*/  

bool Item_sum::register_sum_func(THD *thd, Item **ref)
{
  nesting_map allow_sum_func= thd->lex->allow_sum_func;

  // Find the outer-most query block where this function can be aggregated.

  for (SELECT_LEX *sl= thd->lex->current_select->outer_select();
       sl && sl->nest_level >= max_arg_level;
       sl= sl->outer_select())
  {
    if (allow_sum_func & ((nesting_map)1 << sl->nest_level))
    {
      aggr_level= sl->nest_level;
      aggr_sel= sl;
    }
    /*
      Cannot go above level zero. This might be possible in 5.6 because the
      nest_level of the query blocks of a view are not adjusted when the view
      is attached to the outer query. However, 5.7 adjusts nest_level
      correctly, so this code is only necessary in 5.6.
    */
    if (sl->nest_level == 0)
      break;
  }

  if (aggr_level >= 0)
  {
    ref_by= ref;
    /* Add the object to the list of registered objects assigned to aggr_sel */
    if (!aggr_sel->inner_sum_func_list)
      next= this;
    else
    {
      next= aggr_sel->inner_sum_func_list->next;
      aggr_sel->inner_sum_func_list->next= this;
    }
    aggr_sel->inner_sum_func_list= this;
    aggr_sel->with_sum_func= true;

    /* 
      Mark Item_subselect(s) as containing aggregate function all the way up
      to aggregate function's calculation context.
      Note that we must not mark the Item of calculation context itself
      because with_sum_func on the calculation context st_select_lex is
      already set above.

      with_sum_func being set for an Item means that this Item refers 
      (somewhere in it, e.g. one of its arguments if it's a function) directly
      or through intermediate items to an aggregate function that is calculated
      in a context "outside" of the Item (e.g. in the current or outer select).

      with_sum_func being set for an st_select_lex means that this query block
      has aggregate functions directly referenced (i.e. not through a subquery).
    */
    for (SELECT_LEX *sl= thd->lex->current_select; 
         sl && sl != aggr_sel && sl->master_unit()->item;
         sl= sl->outer_select())
      sl->master_unit()->item->with_sum_func= true;