Hi Adersh,
If your custom porlet is an object based one, creating the required attribute as a MONEY datatype will automatically show the currency column alongside the amount.
If your custom portlet is a query based one, you can use the MONEY datatype in NSQL queries. Just make sure to include the needed currency also in your select statement. This will still allow all the aggregation options. A sample code is given below.
SELECT @SELECT:DIM:USER_DEF:IMPLIED:PROJECT:I.ID:id@,
@SELECT:DIM_PROP:USER_DEF:IMPLIED:PROJECT:'USD':curr@,
@SELECT:DIM_PROP:USER_DEF:MONEY(curr):PROJECT:I.labor_etcsum/3600:ETCSUM@
FROM INV_INVESTMENTS I
WHERE I.CREATED_DATE>'10-MAR-14'
and @FILTER@
Hope this helps.
Georgy