sql - oracle表中的重复总数

Question

我有一张如下表

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

我只需要重复计数（主题||年份），预期答案是 2 而不是

AB1 -- 2
AC1 -- 3

Answer 1

那将是重复查询之上的另一个查询...

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

会给你所有的计数结果。另一个计数这个..

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

应该给你有一个或多个重复的记录数。

Answer 2

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

Answer 3

只需对用于获取示例（AB1，AC1）的查询使用内联视图，如下所示：

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