select * vs select column

Question

If I just need 2/3 columns and I query SELECT * instead of providing those columns in select query, is there any performance degradation regarding more/less I/O

Answer 1

select * from table1 INTERSECT  select * from table2

equal

select distinct t1 from table1 where Exists (select t2 from table2 where table1.t1 = t2 )