GROUP BY using parameters in SQL

Question

I am trying to somehow group a report based on a drop-down list of parameters that is pre-defined. I want to be able to subtotal the Total Hours or Total Pay of my report based on Department or JobCode. I have created the parameters and have no problem with that, I just am not sure if it's possible to use those parameters to call out a grouping command. Below is the spirit of what I am wanting, but the GROUP BY clause doesn't work for me even without a parameter.

SELECT EmployeeID, LastName, FirstName, Department, JobCode, PayRate, SUM(Hours) as "Total Hours", SUM(Pay) as "Total Pay"
FROM Employees
GROUP BY @GroupBy

I am truly a novice when it comes to SQL, so any help is very much appreciated.

Thank You.

Answer 1

The requirement is not 100% clear to me, but I imagine your after something like this:

select
  case when @groupBy = 'dept' then
       department else
       jobCode    end  dept_jobCode,
  sum(hours)
from employees
group by 
  case when @groupBy = 'dept' then
       department else
       jobCode    end;

To be tried with this setup:

create table employees (
  lastName   varchar(20),
  department varchar(20),
  jobCode    varchar(20),
  hours      number
);

insert into employees values ('Miller', 'Dept 1', 'A', 10);
insert into employees values ('Doe'   , 'Dept 1', 'A',  7);
insert into employees values ('Baker' , 'Dept 1', 'B',  4);

insert into employees values ('Sand'  , 'Dept 2', 'B',  6);
insert into employees values ('Stark' , 'Dept 2', 'B',  9);
insert into employees values ('Gild'  , 'Dept 2', 'A',  9);

Obviously, you want to set @groupBy to either 'dept' or any other value.