查詢Oracle資料庫使用者表中的多少資料量

create or replace function count_rows(table_name in varchar2,
                              owner in varchar2 default null)
return number
authid current_user
IS
   num_rows number;
   stmt varchar2(2000);
begin
   if owner is null then
      stmt := 'select count(*) from "'||table_name||'"';
   else
      stmt := 'select count(*) from "'||owner||'"."'||table_name||'"';
   end if;
   execute immediate stmt into num_rows;
   return num_rows;
end;

select table_name, count_rows(table_name) nrows from user_tables