Oracle 11g中的自联接表

Question

Suppose I have a table resulted from a query like this:

+-------+-----+--------------------+-----+--------------------+
|CODE   |CURR |FRONT-END CHARGE    |CCY  |BACK-END CHARGE     |
+-------+-----+--------------------+-----+--------------------+
|002    |AUD  |5.25                |PHP  | 3.75               |
|002    |AUD  |1.75                |USD  | 1.25               |
|002    |BGN  |  14                |PHP  | 8.75               |
|002    |BGN  |   6                |USD  | 3.75               |
|002    |BND  | 9.5                |PHP  |  8.5               |
|002    |BND  |4.25                |USD  |12.75               |
|002    |CAD  |12.5                |USD  | 6.75               |
|002    |INR  |  35                |PHP  |22.75               |
|002    |INR  |  25                |USD  |16.25               |
|002    |YEN  |55.5                |PHP  |16.55               |
|002    |YEN  |77.5                |USD  | 39.2               |
+-------+-----+--------------------+-----+--------------------+

But I want to have a result like this:

+-------+-----+--------------------+-----+--------------------+
|CODE   |CURR |FRONT-END CHARGE    |CCY  |BACK-END CHARGE     |
+-------+-----+--------------------+-----+--------------------+
|002    |AUD  |7                   |PHP  | 3.75               |
|002    |     |                    |USD  | 1.25               |
|002    |BGN  |20                  |PHP  | 8.75               |
|002    |     |                    |USD  | 3.75               |
|002    |BND  |13.75               |PHP  |  8.5               |
|002    |     |                    |USD  |12.75               |
|002    |CAD  |12.5                |USD  | 6.75               |
|002    |INR  |60                  |PHP  |22.75               |
|002    |     |                    |USD  |16.25               |
|002    |YEN  |133                 |PHP  |16.55               |
|002    |     |                    |USD  | 39.2               |
+-------+-----+--------------------+-----+--------------------+

Note that the Front-end charge is the sum of every charges on each of the currency.

I tried using coalesce but it returns the same table when selecting. I also tried self join but the sum on each of the charges becomes different. This is in oracle 11g

Answer 1

This type of transformation should usually be done in the presentation layer -- because the results are not really a SQL table: rows are missing column values.

But, you can do this using window functions:

select code,
       (case when row_number() over (partition by code, curr order by front_end_charge desc) = 1
             then code
        end) as code,
       (case when row_number() over (partition by code, curr order by front_end_charge desc) = 1
             then sum(front_end_charge) over (partition by code, curr)
        end) as front_end_charge,
       ccy, back_end_charge
from t
order by t.code, t.curr, t.front_end_charge desc;

It is important that the outer order by match the order by in the row_number() expressions. SQL queries only return results in a determined order when order by is present.