Custom filter

Hi Folks,

I have a customized form having custom filter i.e Serial number , in my form having data source  "SalesTable" and "SalesLine" like a standard form .

Once serial number selected need to show the related lines and related salesorder in a form .

How can I write a query to fetch reversely from sales line to Sales Table .

Please guide me , thanks in advance.

Regards,

veer