How to get data from data source dynamically

[Victor Lung]

Dear All,
How can i get data from the data source dynamically? can I pass any
parameter to the data source, or I need to set filtering after get the data?
below is what I want to get:
a currency table with From_currency and To_currency, I want to show the
"From Currency" depending on the "To_currency" I selected.

table records:
SGD --> HKD
CNY --> HKD
YEN --> SGD

expected records in the drop-down list box when I selected "HKD" as the
To_Currency:
SGD
CNY

really thx for your help