You can only update a single table at a time, never a join of tables. But
you could do a subquery in the update statement. You haven't specified the
remaining columns in the two tables - I assume there are other columns in
the tables! - so here is an example, created from thin air, that contains
two of the tables in the Sample database:

   Update Department
   set deptname = 'Sales'
   where mgrno = (select empno from Employee where lastname = 'HAAS');

In this example, I want to change the name of a department in the Department
table. For some reason, I can't recall the number of the department but I
know its manager has the last name Haas, which is written entirely in
uppercase in the database. I also know that the MGRNO column in the
Department table contains the employee number of the employee who manages
the department. That enables me to write a subquery which looks through the
Employee table for the employee number of Haas. Then, the outer part of my
Update statement changes the department name for the department that is
managed by Haas.

Assuming your two tables have something in common along the lines of the
Empno/Mgrno relationship, you should be able to write a similar Update
statement so that you can change the ID in Table2 based on the timestamp
value in Table1.

On the other hand, if your two tables really only have the two columns
depicted in your question, you will not be able to do the update you want
because the tables have nothing in common. In that case, you need to
redesign your tables.

--
Rhino

Thw question sounds vague. But i'll take a guess.

UPDATE Table2 SET Value = ?? WHERE EXISTS
(SELECT * FROM Table1 WHERE Id = Table2.Id AND TIMESTAMP = ???)

B.

you can use the following construct:

merge table2  using table1 on
table1.id = table2.id
when matched then
update set value = table1.timestamp

Thanks,
Sumanth