Function table_multi_eq_cond_selectivity

sql/sql_select.cc:11132–11239

*/

static 
double table_multi_eq_cond_selectivity(JOIN *join, uint idx, JOIN_TAB *s,
                                       table_map rem_tables, uint keyparts,
                                       uint16 *ref_keyuse_steps)
{
  double sel= 1.0;
  COND_EQUAL *cond_equal= join->cond_equal;

  if (!cond_equal || !cond_equal->current_level.elements || !s->keyuse)
    return sel;

  Item_equal *item_equal;
  List_iterator_fast<Item_equal> it(cond_equal->current_level);
  TABLE *table= s->table;
  table_map table_bit= table->map;
  POSITION *pos= &join->positions[idx];
  
  while ((item_equal= it++))
  { 
    /* 
      Check whether we need to take into account the selectivity of
      multiple equality item_equal. If this is the case multiply
      the current value of sel by this selectivity
    */
    table_map used_tables= item_equal->used_tables();
    if (!(used_tables & table_bit))
      continue;
    if (item_equal->get_const())
      continue;

    bool adjust_sel= FALSE;
    Item_equal_fields_iterator fi(*item_equal);
    while((fi++) && !adjust_sel)
    {
      Field *fld= fi.get_curr_field();
      if (fld->table->map != table_bit)
        continue;
      if (pos->key == 0)
        adjust_sel= TRUE;
      else
      {
        uint i;
        KEYUSE *keyuse= pos->key;
        uint key= keyuse->key;
        for (i= 0; i < keyparts; i++)
	{
          if (i > 0)
            keyuse+= ref_keyuse_steps[i-1];
          uint fldno;
          if (is_hash_join_key_no(key))
	    fldno= keyuse->keypart;
          else
            fldno= table->key_info[key].key_part[i].fieldnr - 1;        
          if (fld->field_index == fldno)
            break;
        }
        keyuse= pos->key;