Group by vs partition by

Question

Hi,
I am new to my project where I need some help.
My requirement is like below
In EMP table I need to group the all the employees who belongs to one department, I  used group by function to fetch the results, but my lead asked me to use partition by clause. So I am not sure is I get different result set by using partition by ?
If yes How can I use it.
Thanks,

Answer 1

grouping reduces the number of result rows - and analytics do not. Here is a small emp example:
select ENAME
     , job
     , count(*) over (partition by job) job_count
  from emp
order by ename;
ENAME      JOB        JOB_COUNT
ADAMS      CLERK              4
ALLEN      SALESMAN           4
BLAKE      MANAGER            3
CLARK      MANAGER            3
FORD       ANALYST            2
JAMES      CLERK              4
JONES      MANAGER            3
KING       PRESIDENT          1
MARTIN     SALESMAN           4
MILLER     CLERK              4
SCOTT      ANALYST            2
SMITH      CLERK              4
TURNER     SALESMAN           4
WARD       SALESMAN           4
With group by you would only get one line per job group. You could get the same result with a self join with a grouped result:
select e1.ename
     , e1.job
     , e2.job_count
  from emp e1
     , (select JOB
             , count(*) job_count
          from emp
         group by job) e2
where e1.job = e2.job
order by e1.ename;
ENAME      JOB        JOB_COUNT
ADAMS      CLERK              4
ALLEN      SALESMAN           4
BLAKE      MANAGER            3
CLARK      MANAGER            3
FORD       ANALYST            2
JAMES      CLERK              4
JONES      MANAGER            3
KING       PRESIDENT          1
MARTIN     SALESMAN           4
MILLER     CLERK              4
SCOTT      ANALYST            2
SMITH      CLERK              4
TURNER     SALESMAN           4
WARD       SALESMAN           4