Intersect Vs. Join query showing different results.

I have two tables table_a and table_b.

If i do a intersect query. it shows me say 100 records matched.
However, if i do a join it shows me 0 rows matched.

How is this possible. Since intersect and a join are the same thing?


select count(*)
from
(select table_a.col1,
      table_a.col2,
      table_a.col3,
      table_a.col4,
      table_a.col5
from table_a
INTERSECT
select table_b.col1,
      table_b.col2,
      table_b.col3,
      table_b.col4,
      table_b.col5
from table_b);
*******************
rows returned: 100
*******************


select table_a.*, table_b.*
from table_a, table_b
where table_a.col1 = table_b.col1
and  table_a.col2 = table_b.col2
and  table_a.col3 = table_b.col3
and  table_a.col4 = table_b.col4
and  table_a.col5 = table_b.col5

*******************
rows returned: 0
*******************