bool Item_singlerow_subselect::fix_length_and_dec()
{
  if ((max_columns= engine->cols()) == 1)
  {
    if (engine->fix_length_and_dec(row= &value))
      return TRUE;
  }
  else
  {
    if (!(row= (Item_cache**) current_thd->alloc(sizeof(Item_cache*) *
                                                 max_columns)) ||
        engine->fix_length_and_dec(row))
      return TRUE;
    value= *row;
  }
  unsigned_flag= value->unsigned_flag;
  /*
    If there are not tables in subquery then ability to have NULL value
    depends on SELECT list (if single row subquery have tables then it
    always can be NULL if there are not records fetched).
  */
  if (engine->no_tables())
    maybe_null= engine->may_be_null();
  else
  {
    for (uint i= 0; i < max_columns; i++)
      row[i]->maybe_null= TRUE;
  }
  return FALSE;
}
The product constructs all or part of an SQL command using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the intended SQL command when it is sent to a downstream component. Without sufficient removal or quoting of SQL syntax in user-controllable inputs, the generated SQL query can cause those inputs to be interpreted as SQL instead of ordinary user data.