total number of duplicates in oracle table

Question

I have a table like below

SUBJECT Years MARKS
AB      1       20
AB      1       25
AC      1       20
AC      1       30
AC      1       40
AD      1       20

I only need count of duplicates (subject||Year), expected answer is 2 and not

AB1 -- 2
AC1 -- 3

Answer 1

That would be one more query on top of the duplicates query...

select subject, year, count(*)
  from table1
  group by subject, year
  having count(*) > 1

will give you all the results with counts. Another count over this..

select count(*)
  from (
select subject, year, count(*)
  from table1
  group by subject, year
  having count(*) > 1
) 

should give you the number of records which have one or more duplicates.

Answer 2

select subject,years, count(*)
from table
group by subject,years
having count (*) > 1;