Select max field - Mailing list pgsql-sql

I am looking for a way to determine the largest value of a number of fields
in a tuple.

Example:  In a table with the fields id_no, t1, t2 ,t3 ,t4 ,t5
          Select the id_no and the greatest value from fields t1, t2, t3,
t4, t5.

I have tried the following, but with no success:

select id_no, max(t1, t2, t3, t4, t5) from table_1 ;

Anyone have any suggestions?

Thanks in advance for any assistance.

Regards - Bob