Function mysql_derived_optimize

sql/sql_derived.cc:986–1075

*/

static
bool mysql_derived_optimize(THD *thd, LEX *lex, TABLE_LIST *derived)
{
  SELECT_LEX_UNIT *unit= derived->get_unit();
  SELECT_LEX *first_select= unit->first_select();
  SELECT_LEX *save_current_select= lex->current_select;
  bool res= FALSE;
  DBUG_ENTER("mysql_derived_optimize");
  DBUG_PRINT("enter", ("Alias: '%s'  Unit: %p",
                       (derived->alias.str ? derived->alias.str : "<NULL>"),
                       derived->get_unit()));
  if (derived->merged)
  {
    DBUG_PRINT("info", ("Irreversibly merged: exit"));
    DBUG_RETURN(FALSE);
  }

  if (derived->is_materialized_derived() && derived->dt_handler)
  {
    /* Create an object for execution of the query specifying the table */
    if (!(derived->pushdown_derived=
            new (thd->mem_root) Pushdown_derived(derived, derived->dt_handler)))
      DBUG_RETURN(TRUE);
  }

  lex->current_select= first_select;

  if (unit->is_unit_op())
  {
    if (unit->optimized)
      DBUG_RETURN(FALSE);
    // optimize union without execution
    res= unit->optimize();
  }
  else if (unit->derived)
  {
    if (!derived->is_merged_derived())
    {
      JOIN *join= first_select->join;
      unit->set_limit(unit->global_parameters());
      if (join &&
          join->optimization_state == JOIN::OPTIMIZATION_PHASE_1_DONE &&
          join->with_two_phase_optimization)
      {
        if (unit->optimized_2)
          DBUG_RETURN(FALSE);
        unit->optimized_2= TRUE;
      }
      else
      {
        if (unit->optimized)
          DBUG_RETURN(FALSE);        
	unit->optimized= TRUE;
        if (!join)
	{
          /*
            This happens when derived is used in SELECT for which
            zer_result_cause != 0.