SQL Query to get Unique Records from Based on Start Date, Emp Num, Batch

Why do you need to wrap START_DATE within TO_DATE? Is it stored as a string? If it is, can you change that, so it is stored correctly in the date data type? (If it is a date already, then wrapping it within TO_DATE is both unnecessary and dangerous - you may get errors, or wrong results.)

Then: Don't group by UNIQUE_TRANSACTIONID (obviously: you will get different groups for each transaction id, which is not what you need). Similarly, don't group by START_DATE, that makes no sense.

But then, you will not be able to select UNIQUE_TRANSACTIONID in the SELECT list. (Which is probably why you added it to GROUP BY in the first place). Instead, use the LAST aggregate function. The query should look like this:

select max(unique_transactionid) keep (dense_rank last order by start_date) as unique_transactionid,
       batch_number, 
       emp_num, 
       max(start_date) as start_date
from   di_capture
where  [... add your filters here ...]
group  by batch_number, emp_num
;

(And, if needed, wrap start_date within TO_DATE as discussed above.)