Can I query with a select statement in the from statement

Question

I'm working with an application that creates a MASTERTABLE that keeps track of DATATABLEs as it creates them. These data tables are only allowed to be so big, so the data tables are time stamped. What I need to do is to be able to query the MASTERTABLE to find out what the latest datatable is and then query the specific datatable.
I've tried
select count(*) from (select max(timestamp) from mastertable)
and it always comes back with a count of 1.
Is this possible, or is there a better way?

Answer 1

Well, I'm trying to understand... and if I understand, then you need something dynamic. I did create the following example, of course not exactly as yours (I don't have your data). Each employee has a table with his name, containing the sal history, and I want to query that table starting from actual sal :
SCOTT@db102 SQL> select ename from emp where sal= 3000;
ENAME
SCOTT
FORD
SCOTT@db102 SQL> select * from scott;
SAL_DATE         SAL
01-JAN-85       2500
01-JAN-95       2750
01-JAN-05       3000
SCOTT@db102 SQL> set serveroutput on
SCOTT@db102 SQL> declare
  2     v_rc    sys_refcursor;
  3     tname   varchar2(30);
  4     v_date  date;
  5     v_sal   number;
  6  begin
  7     select max(ename) into tname
  8     from emp
  9     where sal = 3000;
10     open v_rc for 'select * from '||tname;
11     loop
12             fetch v_rc into v_date,v_sal;
13             exit when v_rc%notfound;
14             dbms_output.put_line(v_date||' '||v_sal);
15     end loop;
16* end;
SCOTT@db102 SQL> /
01-JAN-85 2500
01-JAN-95 2750
01-JAN-05 3000
PL/SQL procedure successfully completed.
SCOTT@db102 SQL>