Function pushdown_cond_for_derived

sql/sql_derived.cc:1543–1672

*/

bool pushdown_cond_for_derived(THD *thd, Item *cond, TABLE_LIST *derived)
{
  DBUG_ENTER("pushdown_cond_for_derived");
  if (!cond)
    DBUG_RETURN(false);

  st_select_lex_unit *unit= derived->get_unit();
  st_select_lex *first_sl= unit->first_select();
  st_select_lex *sl= first_sl;

  if (derived->prohibit_cond_pushdown)
    DBUG_RETURN(false);

  /* Do not push conditions into constant derived */
  if (unit->executed)
    DBUG_RETURN(false);

  /* Do not push conditions into recursive with tables */
  if (derived->is_recursive_with_table())
    DBUG_RETURN(false);

  /* Do not push conditions into unit with global ORDER BY ... LIMIT */
  if (unit->fake_select_lex &&
      unit->fake_select_lex->limit_params.explicit_limit)
    DBUG_RETURN(false);

  /* Check whether any select of 'unit' allows condition pushdown */
  bool some_select_allows_cond_pushdown= false;
  for (; sl; sl= sl->next_select())
  {
    if (sl->cond_pushdown_is_allowed())
    {
      some_select_allows_cond_pushdown= true;
      break;
    }
  }
  if (!some_select_allows_cond_pushdown)
    DBUG_RETURN(false);

  /* 1. Check what pushable formula can be extracted from cond */
  Item *extracted_cond;
  cond->check_pushable_cond(&Item::pushable_cond_checker_for_derived,
                            (uchar *)(&derived->table->map));
  /* 2. Build a clone PC of the formula that can be extracted */
  extracted_cond=
    cond->build_pushable_cond(thd,
                              &Item::pushable_equality_checker_for_derived,
                              ((uchar *)&derived->table->map));
  if (!extracted_cond)
  {
    /* Nothing can be pushed into the derived table */
    DBUG_RETURN(false);
  }

  st_select_lex *save_curr_select= thd->lex->current_select;
  for (; sl; sl= sl->next_select())
  {
    Item *extracted_cond_copy;