count

SQL> select count(*)
  2  from student
  3  group by dept;

  COUNT(*)
----------
         1
         3
         1

 

   1  select dept, count(*) as num
  2  from student
  3* group by dept

DEPT                                  NUM
------------------------------ ----------
ilectronic                              1
computer                                3
san_gong                                1

SQL>