SQL & PL/SQL

hi all,

I want to use Relational Operator in Where clause but as Parameter, how I can do it? below is the working i tried to achieve but it is showing error

ORA-00920: invalid relational operator

can i use CASE here to check like this:  CASE WHEN :bal = 'G' THEN '>' WHEN :bal = 'E' THEN '=' WHEN :bal = 'L' THEN '<' END

select cust_id, amt from (       
with mytab as (Select 1 cust_id, 100 amt from dual
              union all
              select 1, 50 from dual
              union all
              select 2, 10 from dual
              union all
              select 2, -10 from dual
              union all
              select 3, 50 from dual
              union all
              select 3, -60 from dual
             )
select cust_id, sum(amt) amt 
from mytab
group by cust_id
)
where amt :bal 0

please help.

regards