how to get max value from more than one table

Question

Hi everybody, i had the tables structure like below

Table1
-------
Id SessionNo
1  1
2  2
3  2

Table2
-------
Id SessionNo
1  1
2  3
3  3

Table3
-------
Id SessionNo
1  1
2  3
3  4

from these three tables i need the output as

SessionNo 4

please give me a query for this

Answer 1

SELECT MAX(maxNo)
FROM (
    SELECT MAX(SessionNo) maxNo FROM Table1
    UNION
    SELECT MAX(SessionNo) maxNo FROM Table2
    UNION
    SELECT MAX(SessionNo) maxNo FROM Table3
) r

Answer 2

A possible solution would be (dunno if it is the best).

select max(SessionNo) 
from    
  ( 
     select SessionNo
     from Table1
     union all
     select SessionNo
     from Table2
     union all
     select SessionNo
     from Table3
  )