Method init

sql/item_subselect.cc:79–137

void Item_subselect::init(st_select_lex *select_lex,
			  select_result_interceptor *result)
{
  /*
    Please see Item_singlerow_subselect::invalidate_and_restore_select_lex(),
    which depends on alterations to the parse tree implemented here.
  */

  DBUG_ENTER("Item_subselect::init");
  DBUG_PRINT("enter", ("select_lex: %p  this: %p",
                       select_lex, this));

  select_lex->parent_lex->relink_hack(select_lex);

  unit= select_lex->master_unit();

  if (unit->item)
  {
    engine= unit->item->engine;
    parsing_place= unit->item->parsing_place;
    if (unit->item->substype() == EXISTS_SUBS &&
        ((Item_exists_subselect *)unit->item)->exists_transformed)
    {
      /* it is permanent transformation of EXISTS to IN */
      unit->item= this;
      engine->change_result(this, result, FALSE);
    }
    else
    {
      /*
        Item can be changed in JOIN::prepare while engine in JOIN::optimize
        => we do not copy old_engine here
      */
      unit->thd->change_item_tree((Item**)&unit->item, this);
      engine->change_result(this, result, TRUE);
    }
  }
  else
  {
    SELECT_LEX *outer_select= unit->outer_select();
    THD *thd= unit->thd;
    /*
      do not take into account expression inside aggregate functions because
      they can access original table fields
    */
    parsing_place= (outer_select->in_sum_expr ?
                    NO_MATTER :
                    outer_select->parsing_place);
    if (unit->is_unit_op() &&
        (unit->first_select()->next_select() || unit->fake_select_lex))
      engine= new (thd->mem_root)
        subselect_union_engine(unit, result, this);
    else
      engine= new (thd->mem_root)
        subselect_single_select_engine(select_lex, result, this);
  }
  DBUG_PRINT("info", ("engine: %p", engine));
  DBUG_VOID_RETURN;